she may have some sort of lice or ticks. She might not be getting enough vitamins and minerals in her diet, try feeding her alot of green vegetables and some fruits, but peel the fruits first(even if it apple or grapes)because the peel will cause diareia.ALso give her dry
kitten food this will give her all the protein she will need, give a few peices of it to her in her food each day. And make sure the mouse eats it, try not giving her any other foods then this for one day, it shouldnt hurt her, the worst it could do is make her better. Please updat on how she is doing

i hope she gets better