Rocky(11yrs old) has no trouble sitting,walking,running,but he went from 16lb's to 12lb's in a very short time,in losing so much weight,he also lost musclemass.
I don't think he's arthritic,but I am no vet...I just don't want to give him painpills if it seems he does not need it.
I hope your little girl will do ok,it's a worry when they don't drink,luckily all of mine drink quiet a bit,I change the water about 15 times a day
I had a waterfountain once,but they were afraid of it