So there's this hot girl, but she used to be fat...

There's actually a lot more to it than people think. Absolutely nothing gives you a confidence and self esteem boost like losing weight. I know cos I've been there. So the girl is most probably very confident if she's *recently* lost weight. If she did it many years ago then there's no real difference. Depending on how big a transformation it was, she's either got a really nice personality or she's a total bitch. If she became super hot, she's most likely a bitch. She went from getting mocked to getting loads of attention from guys, she'll be arrogant. People might say I'm generalising, but its psychological. The emotional effects of getting bullied aren't nice. When you suddenly go into a position of high power, you abuse it.

What do you mean by fat? You shouldn't call her fat, even if she was 'bigger' before. Anyone can become slimmer or bigger if they want (or unintentionally), therefore it shouldn't really affect anything.