I'd ask her if something is going on at school that is upsetting her. It seems she changed her behaviors drastically after school started.
School is a very controlled environment.
Thinks could be happening with other kids.

When my daughter started first grade, she had older boys asking her very inappropriate sexual questions on the bus. I could tell by her acting out behavior something was wrong. While starting school is a huge adjustment for kids, sometimes bad things could be happening too.
Good luck! Parenting is hard, if you are doing it right.