Poorly rat very very thin?

I have 10 rats just cleaned ou there cage and noticed that one of them is very very thin I can feel her ribs I can't get her to vet tonight should I separate from others and give extra food eg rice pudding or something similar or leave in with others very worried as she is normally very skittish and is very docile :( she is eating just given her a chic drop and some other food so not sure if others are pushing her away from food please help