I think she should have stopped and the incident wouldn't have been so bad if she'd have checked to make sure he was okay, said sorry and didn't make rude tweets about it.
I just liked the interview they did with her. "Erm, yeah, I did stop, I did stop! But like, he wasn't wobblin' or anythin'" yadda yadda. Poor girl as she was probably frightened, but still; you. just. hit. someone. with. your. car - and then tweeted about it.