The real reason is unknown. I mean it was cosmectic surgery but what exactly gone wrong? Many does cosmetic surgery and have no problems or at least don't die. And many more surgeries. Is like an everyday procedure most of them. People die everyday for the most random reasons.
It doesn't work like that. She used to be a fighter so probably she had a weight class to hit. When woman losses too much weight their boobs go away. Once they gain their weights back their boobs come together.