I'm bad at judging what feeder size should be from pictures, but the feeder should be the same circumference as the widest part of her body (or enough smaller feeders to be the same weight as an appropriately sized one). She looks pretty thin to me too.

Cluttering up her tank and upping her food intake should help. Also, they have pretty bad eyesight, and young ones are more nippy than adults. She'll probably grow out of some of it.