Cat has a cold, or maybe allergies. When to see a vet?

So yesterday I noticed Ida's nose was making a whistling sound and today she sounds a bit stuffier. When she's resting the sound is just a quiet whistle, but when she exerts herself, her breathing sounds quite strenuous. Apart from the stuffy nose she seems perfectly normal. No change in appetite or anything else.

What I'm wondering is should I take her to the vet over this? I don't want to put her health at risk but I also don't want to stress her out over sniffles. I don't drive so getting to the vet takes nearly an hour by bus, which would be stressful enough, but since she won't let anyone touch her, she would need to be tranquilized for the vet to check her.

Her vaccinations should be valid until summer, so I guess it could just be allergies. I've had allergy symptoms for a few days now, so maybe that's it?

Since her appetite is good, I would just keep a close eye on her.  One of my ferals was sick around Thanksgiving time.  He was making a coughing sound and strange whistle like breathing.  I was so worried about him.  Yet he too ate and drank water and even played with his buddy a bit.  He slept a lot too.  I debated back and forth whether to try and get him to the vet.  I knew that if I trapped him he would never go near the trap again.  It had been 4 years since I did TNR on him and he had forgotten about the trap.  Yet I wanted to save re trapping for a real emergency.  I decided to wait and watch.  He never got worse, but it took over a week for him to get better. 

Just use your best judgement.  You could even call the vet and talk with them and see if they have any suggestions.

Thank you for the advice! I'm quite certain now that she just has allergies since she hasn't developed more symptoms. I called the vet and she recommended cortisone pills to begin with and then zyrtec for maintenance. I managed to slip the cortisone to her earlier today and now I'm watching and waiting. Her symptoms had already improved a bit on their own, probably due to the rainy weather we've had for a couple of days. She's hasn't had hay fever before, as far as I know, so I wonder if becoming an indoor cat has made her more sensitive.

I actually had the worst brain fart ever a while ago as I thought to myself: "I hope she's not allergic to cats, because that would suck"... I'm going to put that down to a long day at work depleting my thought capasity

If she has the sniffles and sneezes, she likely has a cold. Most cat colds are caused by one of a few viruses that cats get, and resolve on their own after a few weeks. If the cold doesn't resolve after a month, if there is discharge from the eyes, or if lethargy/fever sets in, then the cat usually needs an antibiotic. 

If your kitty worsens, you can discuss the situation with your vet over the phone and perhaps take a picture or video of your cat and email to the vet. If your cat needs an antibiotic and getting her to the vet is an ordeal, one that requires sedation, then it's possible your vet may just prescribe the antibiotic for her without an appointment. The vet clinic I use for my ferals has done this for me for my outdoor feral on a few occasions when it was clear from the pictures I emailed and the symptoms I described that an antibiotic was needed. Vets who work with ferals are usually more understanding about these situations, and will prescribe a needed medication for a cat who is known to them without having to see the cat again. I just wanted to let you know that this may be an option.

Hopefully your kitty does have a virus, which will resolve, rather than an allergy which would be ongoing.   

Thank you for the tip. Must keep it in mind for the future

The cortisone did the trick so it seems, unfortunately, that Ida is quite allergic. I suppose now the only thing to do is to find a medication schedule for her. I would like to avoid feeding her allergy medication on a daily basis, so maybe I'll try every other day to begin with. The vet told me to give 0,2mg/kg of zyrtec, and with Ida being about 3kg that's like 0,6mg, but I only found 10mg pills. I'm going to have to go all microsurgery on that thing! Oh well, whatever it takes to keep her feeling well