It's so great that she's looking good and has turned into a good eater, esp after her rough start! I'd go by body condition, not the number on the scale. As long as she looks proportional and is growing, that's what matters. Slow growth is better in the long run anyway. Two other thoughts:
Are you sure she's a "she"? If I'm remembering right, you got her at a pet store, but I don't remember who sexed her for you? Males are generally smaller, so that could be one explanation.
What size rodent is she on? Most of ours have relatively slow growth until they get on weaned rats. Then they seem to fill out pretty nicely. It could just be that she is still working up to a larger prey size.