Hello Jessica, I'm Dr. Deb. I'll do my best to help you today.
I'm sorry for this concern for Dolly; I can see that you're quite worried about her.
To specifically answer your question, yes, fevers are fairly common in cats.
They can certainly be secondary to bacterial infections or viruses such as Leukemia, Feline AIDS and FIP. Toxoplasmosis is a protozoal disease which can also cause cats to run fevers.
Auto immune diseases cause them as well .
Unless there are other symptoms such as weight loss, pale gums, abdominal fluid, respiratory issues, neurologic signs, etc, then I wouldn't immediately jump to the conclusion that she has something serious.
There's a condition in cats that is called Fever of Unknown Origin- which is exactly what it sounds like. Cats are running a fever but we can't find an explanation for the elevated temperature. Treatment is primarily supportive which consists of fluids and drugs to reduce the fever although every vet has their own protocol as to how they treat these cats. Most cats recover fairly quickly.
I might give the drugs a chance to work before I'd take her back for a recheck but given your concern for her, if she's not significantly improved by tomorrow, you might want to pursue testing then.
When I see these cases, if the fever doesn't resolve within a day or two or if it recurs, then I recommend additional testing at that time.
I hope this helps and eases your mind about this somewhat. Deb