09/17/2011 at 01:00 PM EDT
Kara Kennedy, the eldest daughter of former Senator Ted Kennedy
, and sister of Patrick Kennedy, died suddenly on Friday, the family confirms. She was 51.
She was working out in a Washington D.C.-area gym at the time, the Associated Press reports.
"She's with dad," Patrick Kennedy said. Their father died in 2009
at age 77 after battling a brain tumor.
Kara, who helped work on her father's senatorial campaign, was also a cancer survivor. In 2003, she had a malignant tumor removed from her lungs. According to her brother Patrick, the cancer treatment "took quite a toll on her and weakened her physically. Her heart gave out."
Kara, who was divorced, is survived by her two teenage children.