Awe! She's so precious! Good for you for taking care of her, most people wouldn't! Anyway, back to your questions!
1.) Have you tried feeding her with a needless syringe? I'm not really sure what these are called, but people use them to feed small children medicine, this way you can also measure how much food you are giving her. They are common household objects, but if you happen not to have one, you can get them at most drug stores or you can use an eye-dropper. She may respond to those better
2.) I am not 100 percent sure of this question but bear with me. It may be a normal digestion cycle for infant mice. Since you think she is getting skinnier, she may have not ate much. You should keep trying rubbing her belly after she eats if the concern continues.
Good Luck with your little baby girl!
Ming (pug) 13 years
Mei-Mei (pug) 4 years
Teagan (Gerbil) 2 months old