Meet Our
Leadership Team

Dennise Erwin, MBA

Chief Executive Officer

Dennise Erwin is the CEO of Horizon Medical Center of McKinney. She is responsible for leading the organization with a dynamic leadership style shaped by over 20 years of experience in the healthcare field. Dennise places a strong emphasis on open communication, believing that explaining the “why” behind decisions helps employees understand, accept, and align their goals with the organization’s direction, fostering a cohesive and motivated workforce.

Dennise grew up in North Texas and served honorably as a United States Marine from 2000 to 2004 as a Disburser. While serving, she completed her bachelor’s degree in health care administration from Southern Illinois University Carbondale. She then pursued an MBA from the University of Phoenix, graduating in 2006 while working as an Administrator for a Home Health and Hospice organization.

Following her MBA, Dennise was promoted to VP of Clinical Reimbursement and later advanced to President of the same organization. In 2022, she transitioned into the hospital setting as CEO, where her leadership continues to make a positive impact.

In her free time, Dennise enjoys running, hiking, and traveling with her family. She has been married for 24 years to a retired United States Marine, and they have one son. Their family is rounded out by three furry companions: Jack, Penny, and Bruno.

Stefani Forsythe, CPA

Chief Financial Officer

Stefani Forsythe serves as the Chief Financial Officer for Horizon Medical Center of McKinney, where she is responsible for overseeing all aspects of the company’s financial management. Her extensive duties include accounting, corporate treasury, financial planning and analysis, insurance, and tax. 

Stefani graduated from Southern Methodist University with a bachelor’s of business administration in accounting. Stefani brings over 30 years of experience in financial management, business leadership, and corporate strategy, including nearly two decades within the healthcare industry. Her deep understanding of financial operations in complex, high-stakes environments has been a cornerstone of her leadership at Horizon Medical Center, where she plays a pivotal role in aligning financial strategies with long-term organizational goals. Throughout her career, she has been recognized for her ability to balance detailed financial oversight with a forward-thinking approach to corporate growth.

In her free time, Stefani enjoys an active lifestyle. She loves spending time with her husband and their beloved fur babies, while also making time for travel, running, and hiking adventures.

Dr. Maynard Dela Pena, PT, DPT 

Director of Rehabilitation

Dr. Maynard Dela Pena is the Director of Rehabilitation at Horizon Medical Center of McKinney, where he leads an exceptional team of therapists dedicated to helping patients achieve their rehabilitation goals. With a strong belief in patient-centered care, he focuses on providing personalized treatment plans that empower individuals on their recovery journeys.

Dr. Maynard earned his Bachelor’s Degree in Kinesiology from Texas Woman’s University before pursuing his Doctorate in Physical Therapy from the University of Texas Medical Branch at Galveston. With over a decade of experience in the field, he possesses a unique blend of skills that includes not only physical therapy expertise but also experience in marketing and hospital administration within the inpatient rehabilitation setting. Each of these roles has significantly contributed to his ability to deliver the highest standard of care to his patients.

Known for his caring and empathetic nature, Dr. Maynard takes immense pride in supporting each patient’s path to recovery. Outside of his professional responsibilities, he enjoys spending quality time with his wife and two children, actively participating in their recreational and club sports activities. This balance enriches his life and enhances his commitment to holistic patient care.

Sawyer Powers-Ferguson, PT, DPT 

Director of Business Development

Sawyer Powers-Ferguson is the Director of Business Development for Horizon Medical Center of McKinney. She is responsible for building partnerships and expanding the medical center’s presence and influence in the healthcare community and surrounding areas. Additionally, Sawyer and the team of liaisons at Horizon Medical Center have the privilege of guiding patients from their acute care stay into the next phase of their journey in inpatient rehabilitation. 

Sawyer earned her bachelor’s degree in social work from Texas Christian University and went on to receive her Doctorate in Physical Therapy from Rockhurst University in Kansas City, Missouri. She has over ten years of experience in the field of physical therapy primarily in the hospital setting. Since 2018, she has shifted focus to non-clinical roles, starting as a clinical liaison, promoting to management, and more recently, spending the past two years in an educational capacity within the pharmaceutical industry. Each role has allowed her to serve and advocate for patients in a different capacity. Sawyer believes that knowledge is empowering and takes pride in helping patients and families understand what lies ahead in their recovery.

In her free time, Sawyer enjoys spending time with her husband and daughter, regularly attending TCU football games.

Karely Weinmann De Leon, MSN, APRN, FNP-C

Chief Compliance Officer

Karely Weinmann de Leon is the Chief Compliance Officer at Horizon Medical Center of McKinney, where she oversees compliance with regulatory standards and ensures that the facility upholds the highest ethical and legal practices in inpatient acute rehabilitation. She is responsible for implementing policies that safeguard patient safety, privacy, and quality of care, while also promoting a culture of accountability throughout the organization.

Karely earned her Bachelor of Science in Nursing in Mexico and later completed her Master of Science in Nursing with a focus on Family Nurse Practitioner at the University of Texas at El Paso. With her extensive clinical background and strong leadership in compliance, Karely is dedicated to maintaining the integrity of healthcare operations and supporting continuous improvement across the rehabilitation setting.

Outside of her professional role, Karely is passionate about spending time in nature. She enjoys hiking, reading, and caring for her collection of plants, finding peace and balance through her love of the outdoors.

Dr. Malik Mohsin Ali, DO

Chief of Staff/Internal Medicine

Dr. Malik M. Ali, D.O., serves as the Chief of Staff and consulting hospitalist for Horizon Medical Center of McKinney. He plays a key role in supporting the hospital’s mission to provide exceptional care for patients. Alongside a dedicated team of healthcare professionals, Dr. Ali ensures that patients receive compassionate, personalized care as they move through their hospital stay, rehabilitation, and ultimately return home.

Dr. Ali holds a Bachelor of Arts in Biology from Baylor University and a Doctor of Osteopathic Medicine from The University of North Texas Health Science Center at Fort Worth. His early experience working in his father’s small business instilled in him a strong work ethic, a commitment to ethical practices, and the importance of forming personal connections. These principles shape his approach to medicine, helping him build trust with his patients while guiding them through significant health challenges. For Dr. Ali, the most rewarding part of his work is seeing patients overcome obstacles, regain their health, and return to the people and activities they love. 

Outside of work, he cherishes time with his wife and three children, particularly through their shared love of travel and exploring new destinations as a family.

Dr. Ahmed Mahmoud, MD

Medical Director of Rehabilitation/PM&R

Ngozi Chatterton, RN, MSN, CMSRN

Chief Nursing Officer

Ngozi Chatterton is the Chief Nursing Officer for Horizon Medical Center of McKinney, where she oversees all nursing and clinical care, ensuring patients receive safe and high-quality treatment during their hospital stay. Her dedication to patient-centered care is reflected in her commitment to evidence-based nursing practices and her passion for involving patients and their families in every aspect of their care plan, promoting confidence and comfort throughout the hospital experience.

Ngozi comes from a family of medical professionals and began her healthcare journey as a care technician in her father’s hospital. She started her nursing career earning her LVN from North Central Texas College, ADN from North Texas Central College, BSN from the University of Texas, and MSN in Nursing Administration and Leadership from Western Governors University.

Ngozi is passionate about being part of a team that helps individuals return to their best possible selves through personalized care, education, and advocacy. Her leadership in nursing is driven by a desire to ensure that every patient has a positive and supportive experience.

Outside of her professional role, Ngozi enjoys spending time with her family, including two daughters in college, a son in middle school, her mother, and her beloved fur baby.

Jennifer Manzanera, MBA

Chief Human Resources Officer

Jennifer Manzanera is the Chief Human Resources Officer for Horizon Medical Center of McKinney, where she focuses on all aspects of the employee life cycle. With over 20 years of HR experience across various industries—including manufacturing, hospitality, advertising, and healthcare—Jennifer brings a diverse perspective to her role.

She holds a bachelor’s degree in human resources from Miami University of Ohio and a master’s degree in business administration from the University of Phoenix. Jennifer is dedicated to fostering a positive workplace culture and implementing strategic HR initiatives that enhance employee engagement and organizational effectiveness.

Outside of her professional endeavors, Jennifer enjoys spending time with her active family and their German Shepherd, and cheering on the Clemson Tigers and Pittsburgh Steelers.

Petra Zamora, PharmD, RPh.

Pharmacist in Charge

Petra Zamora is the Pharmacist in Charge at Horizon Medical Center of McKinney. She is responsible for overseeing the hospital’s pharmaceutical services, ensuring safe, effective medication management while advancing clinical practices. After earning her Doctor of Pharmacy from Albany College of Pharmacy and Health Sciences in New York, Petra began her career at a community pharmacy, but soon transitioned to an inpatient clinical pharmacist role at a 400-bed hospital in Dallas. Over the years, she has gained extensive experience in large healthcare systems, where she has been instrumental in expanding clinical functions and ambulatory services. As a clinical pharmacy specialist, she has managed hospital formularies, developed protocols, and led pharmacy teams, ensuring precise medication management through pharmacokinetic calculations and strict adherence to regulations.

In her free time, Petra enjoys playing the piano, cooking, and exploring new cuisines with her husband and children.