Why is my best friend treating me like crap?

Your "best" friend sounds very arrogant, and if she doesn't appreciate you fully, then no doubt someone else will! So just give her a taste of her own medicine, deny her of spending time together whenever she wants, giving her money,and she'll get the drift and won't like it. If she doesn't realise her wrong doing, then she's not worth your time. Best of luck :)