Wait wait wait - they outgrow this!!!!!!! Dang, can someone tell my 14 year old that? LOL actually since I have invested a ton of money in his mouth for braces this month he is actually brushing and everything.
Obviously, brushing was an issue in my house. I bought him a variety of toothbrushes when he was little - usually let him pick them out himself. He liked the ones that played music. Some had music on a "timer" and he brushed while the song played. We also did electric toothbrushes (still do). But there where times when I had to basically sit on him and brush his teeth. We brushed our teeth together, and made a rather gross game out of rinse and spit - but hey, I am raising a boy and they are just more gross than little girls.
M., we all go through this. I think the important thing is that you are teaching dental hygiene to your daughter and this will get easier as she gets older. At her age the attention span it just not there to hang in and brush for the recommended two minutes. Do you floss her teeth? My hygienist gave me a tip years ago, when my son was little, to do that right before bedtime, when he was sleepy. He would lay with his head in my lap and I would floss for him. It worked well.
You are doing all right things.