Cannot tell from photo online...but she might be, as I said earlier, & mice age pretty fast. I wonder if she had been used for breeding before sold as a pet? That matters.
But age or illness, I really wouldn't bet on her living long att. When they lose weight like that, & their sides get a little concave & they breathe like that, it doesn't end well. Sorry...I doubt a vet can do much att, but it's up to you if you want to try, or feed a special diet, etc. All the best...
Thank you. I’ll see how she is tomorrow and then decide. But so for there has been no improvement .