I think the only thing you can really do is take her to the vet as soon as possible. If (and I'm not saying it's definitely the case) she needs to be put down, it will only be because she's suffering. And if she has some sort of illness, which is very likely, it would be best to get it treated quickly. Chances are it's something easily curable, but leaving it too long would be dangerous.
I'm really sorry she's sick, I know it can be extremely upsetting when a pet is ill.
But try to stay positive. Even the most alarming illnesses can often be cured. Get it checked when you can and I honestly hope everything turns out well.