Meg, I just read this post .
My cat Rue just had what sounded like congested breathing and nothing else.
When I first took her to the vet, he gave her ammoxicillin (sp?) and she started to sound better after about a week.
When the meds were finished, she was back to sounding congested after about 2 days.
I took her back in and the vet gave a stonger antibiotic. She was on that one for 3 rounds in a row, with her being checked each time just before the round of antibiotics were finished.
With an upper respiratory infection from what I understand, they can have several different symptoms and it is hard to find just the right antibiotic to treat it. it is also a stubborn virus.
Once treated , this virus has a tendency to go dormant in the cat's body and will return if the cat is highly stressed.
I am not a vet, so I may be wrong by saying this, but I would wait to have her spayed till she is totally over this thing and has had a chance to regain her strenght.
This would be something that I would discuss with my vet, just to make sure she can handle the operation as it is major surgery.
IF you decide to wait till she 's stronger, just make sure she doesn't end up pregnant !
Btw, my little Rue is fine now (finally!), she is a bundle of energy, and very loving and talkative,lol.
A few days after she finished her final antibiotics she started growing like a weed .