The Pegula family announced on June 14 that she was "receiving medical care as a result of some unexpected health issues."
Pegula has been the co-owner of the Bills since 2014, when she purchased the franchise with her husband, Terry, for more than $1 billion.
The pair also own the NHL's Buffalo Sabres, making Pegula the first woman to become president of both an NFL and NHL team.
"We are grateful for the medical professionals providing her care and to everyone for their prayers and well wishes," the Pegula family's statement, posted on Twitter, continued. "We ask that you please continue to respect our need for privacy during this time."
The Bills team has rallied around Pegula.
"All of our thoughts and prayers are with Kim and the Pegula family," said coach Sean McDermott when news of her health issue was first announced. "They've done so much for me, my family, our team and the city of Buffalo."