Cat at vet, called and said she is running high temp--any ideas?

One of my outside dumped kitties that had a litter of kittens last year (she showed up heavily pregnant) finally let me get her and take her in for a spay.  She was spayed yesterday, and the plan was for them to keep her until Monday evening so she has a while to rest and heal. 

A few minutes ago the vet's office called me to tell me she is running a fever of 104.3 (which absolutely scared me to death).  They tested her for FLV and FIV and both were negative, and did pre-surgery bloodwork that was okay.  I had told them I had noticed the past 3-4 times I had seen her at the house before bringing her in she had diarrhea and I could see a bit of her inner eyelid, but they related this to the positive stool test for parasites/worms and went ahead with the spay.

They said they are going to do a urine catch as it could be a UTI, and I asked about other possible reasons.  She said it could be from the surgery, could be a reaction to the vaccines, the parasite/worm meds, any/or all.  I'm worried sick.  I am really attached to this little lady, as I have worked and worked with her for the longest, cared for her kittens, found them homes.  I had (unbeknownst to my hubby, well, he probably guesses) plans on bringing her inside to live.

Has anyone been through this?  I'm just worrying myself silly.  But I'd rather know the possibles than be blindsided by a call from the vet with the worst.

They did tell me she seems fairly happy, interacts with them well, and is eating very well.  They said she has eaten all her food today and they have already fed her twice.

It could also be an infection of unknown origin and will respond to appropriate use of nsaids, fluids etc.

Thanks StephenQ....they did tell me she is still on IV fluids, and they were going to give her something for the fever and pain medication as well.  I'm just obsessing, hopefully (probably) unnecessarily, but I can't help it.  She is a little sweetheart.  I saw her yesterday not long after she was in the recovery area, and she was fairly alert and responded to me, just a bit stoned. 

At least it was encouraging that she is eating so well, and she responded well to them calling her name and talking to her.  The tech that called me said she is acting quite fine, just running the temp.  I'm just scared.  They did tell me that they would update me tomorrow morning first thing with urinalysis and blood panel results, that they would probably do a blood panel again tomorrow too.

I hope she's ok!! Maybe a little stressed from the surgery? When I took my cat in to the vet last week she had a temperature of 104F and was mildly dehydrated. She wasn't exhibiting other symptoms of being sick besides that and lack of appetite and told me they would monitor her throughout the day. Well a few hours later they called me to say that her temp returned to normal and she was given sub q fluid. I picked her up a few hours after that and the fever didn't return. They told me it could have been stress related.

Sending you both good energy!! 

Thank you both! Today her temp is back to normal, and she is doing well! She is still on her IV as a precaution, and they are going to give her fluids until tomorrow for support. Her bloodwork was good, urinalysis was good...so hopefully little prissy paws will be fine to come home Monday evening! I guess I'm so used to male cat neuters, I just went insane with worry over this little lady. I'm rather attached to her!