have you given her the chance to pick out a toothbrush that she likes? There are also children books ( I saw one in Big W today but cant remember the name of it) that if she reads it and does the actions with you might help.

I sit my DS on the bathroom bench and we brush our teeth together. I put a little of his toothpaste on my brush too so when he decides mine is better he is still getting the right paste. HTH