Is my mouse dying? Please Answer soon!?

My mouse is about a year old now and she was very active. now i noticed that she was slowing down and was getting red around the eyes and some kind if fluid. we took her to a vet and he gave us eye drops. (he had no clue what he was doing) it progressively got worse. now she looks like she's dragging her rear end, she wont move or eat and hardly drinks water.... i think shes had a respiratory infection because i didn't change her bedding for 2 weeks at one point... if she is dying how can i comfort her without euthanizing her? is she dying of old age or what?