harrison went through this stage and he still eats really really slow, what it was with him is that he couldn't be botherd to sit and eat. All i did was him was make it clear that he had to eat all his tea no matter how long it took him, even resorting on a few occasions to warming his food back up until he had eaten enough.
As long as she is eating all her meals i'm guessing in time she will start to eat faster, i guess its just a phase as most of my friends have had the same problem with their children.