Have you tried live rat pinks? I know live hoppers are usually what's taken first but try live rat pinks. Try a hide box and leave the rat pink in over night.
If it was born small the weight may be deceiving. If the snake seems solid I don't worry so much but don't let it get too skinny.
I forgot to mention they all have hides as well. I mean I guess she seems healthy but at the same time is really skinny.