B.K.
Well first I think her dad needs to tell her that she must obey you in regard to the brushing, since he's not home when she does it.
Second, if she were my kid we'd stand there until she properly brushed her teeth. You're the adult and she's the kid, so you're running the show not her. I can outwait anybody -- I'd bring a crossword puzzle to work on if I had to. And we'd stand there together until it was done.
Third, my dentist suggested that my daughter brush her teeth for the length of a song on a cd. So when she was little, she'd pop in her favorite cd and play a song and brush until it was over. Maybe that would make it a little more fun for her.