First appearing to the Parkers when she was only 13, Kristy idolized her cousin, Mary Jane Watson, and wanted to be a model just like her. She said her parents sent her to live with Mary Jane and Peter Parker while they vacationed in Europe. At first they accepted her, though they knew she'd make it harder for Peter to sneak in and out as Spider-Man.
Soon she began to show symptoms of bulimia, though at the time nobody really noticed. Once, Mary Jane joked about how jealous she was that while Kristy ate large amounts of food, she never seemed to gain any weight.
When Jonathan Caesar had Mary Jane evicted from their apartment, Kristy followed along as they moved in to Peter's Aunt May's house. After Peter and Mary Jane found a new place to live, they made Kristy, albeit reluctantly, stay behind with May. She continued binging and purging her food, not noticing that her weight was dropping alarmingly. It was a panicked May Parker that called for an ambulance when she discovered Kristy passed out on the bathroom floor. She was taken to Queens Medical Center where she was told that she had bulimia, but to Kristy, it was all a sick joke and she honestly believed that she was gaining more weight.
Her parents finally came to see her, and they were anything but sympathetic. Her father was verbally abusive, calling her illness a bluff to get him to waste more of his money on her. All her mother did was talk about the wonderful time they had on their European trip, seeming oblivious to her daughter's condition. Mary Jane angrily scolded them for treating Kristy so horribly when she was obviously sick, and her father retorted that, since she thought she knew what was best for the girl, that she could take over caring for her from now on. Kristy was happy that someone finally stood up for her, and she tearfully told Mary Jane that she'll try to stop being so much trouble for her and Peter.
She seems to have her bulimia more under control since then, and hangs out with her cousin in their apartment as often as she can.