As the mother of a 21 yr old son who moved in with his dad for his senior year in high school and became so much like him that when his dad kicked him out the day he turned 18 and he moved back in here, it lasted 2 months and I could no longer take his total disrespect for me, his sister, any rules, etc. He left for college 2 months later (whch only lasted a few weeks) but he stayed in the other town about 2 hrs away because I said no he couldn't move back in here. His occasional visits have shown he hasn't really grown up to much yet and in fact living on his own has made him even more like his dad. I really can't live with that.

hang in there......be firm with rules and responsibilities especially a job at the age of 21 since she isn't going to school.
Take care of yourself