Try these 4 steps:
1) Brush in front of her. Your one of her biggest examples and a lot of what kids learn are from their parents at this age.
2) Make it a fun nightly (and maybe even morning) family event. You can look into fun toothbrushes online that she may get a kick out of.
3) It might be the type of toothpaste. Make sure your using a kids brand as those are less abrasive than adult brands. Also look into different flavors, try it out if she does not like a flavor move to another one.
4) Make sure to reward positive steps in the right direction and ignore the negative ones. Positive reinforcement can be as simple as saying “great job brushing your teeth!” Believe me it goes a long way. My job is to get children to cooperate and enjoy their dentist appointments. Positive reinforcement is one of the greatest tools.