Hello Julie, I'm Dr. Deb and I'll do my best to help you today.
I'm sorry that Bonnie has been diagnosed with an upper respiratory infection although I'm glad that she's responding to treatment thus far.
There are several ways you can help with her stuffy nose:
1. Use warm water to clean the nose of any discharge that builds up.
2. Nasal decongestant drops can be helpful although many cats don’t like them very much as you can imagine. The medicated ones should only be used for three days in a row, with one drop in each nostril; otherwise what’s known as a rebound effect may occur. Examples include:
a. Pediatric otrivin=0.05% xylometazoline
b. “Little Noses" Decongestant Nose Drops with phenylephrine hydrochloride
c. Afrin (oxymetazoline)
d. "Little Noses" Saline Spray/Drops non medicated which can be used more than three days in a row.
3. You can place her in a bathroom with hot water running so that the steam can loosen up secretions or run a humidifier instead.
4. Antihistamines are not typically effective for this problem in all cats but does appear to help dry up secretions for some. Options include:
Benadryl at a dose of 1/4 of a 25 mg tablet given twice daily or
Chlorpheniramine at a dose of 2 mgtwice a day or
Claritin at a dose of 2.5 mg twice or
Zyrtec 2.5 mg once or twice a day
It is important to ensure that the formulations used contain ONLY the antihistamine and are not combination products (e.g. Claritin-D contains pseudoephedrine, which could cause very significant adverse effects in a cats.
Sedation is a common side effect with these kinds of drugs so I wouldn't want you to think she was worsening if you decide to try them.
The good news is that most Upper Respiratory Infections only last 10-14 days in most cats so, hopefully, she should be over this soon.
I hope this helps. Deb