I'd feed her the same (small adult mouse) for a while...see how she does. Her digestion might be slower than you think right now...see IF she's hungry in a
week...it might take 10 days or 2 weeks before she's ready to eat again. Just see how she does, take your cue from her, ok? I know how badly you want her
to put weight on, but better to do it slowly...especially since you have no medical history on her. For example, IF she is skinny because of internal parasites,
when you feed HER a bigger meal, you also feed THEM a lot more, & that can harm (even kill) the snake if -IF- they expand & block essential functions. See?
As I said before, her weight probably has nothing to do with parasites & everything to do with a negligent owner, but no way to know just yet, so go slow.
Have you looked closely for mites too, btw? A skinny snake can get dehydrated & die much faster from mites than a healthy one...so hopefully no mites.