My cat is sneezing with discharge after surgery. Is it serious?

Hi Laila! It could simply be she has a respiratory infection, and I wouldn't get too worried about pneumonia just yet. Signs of pneumonia include labored breathing, loud respiratory sounds, lethargy, reduced appetite, and fever. If she doesn't have those signs as well, I would be more suspicious she has a respiratory infection. I can give you some things to try at home for Kitty. First, you can try starting her on an L-lysine supplement - this is an amino acid that has been shown to help the immune system fight off respiratory infections more effectively. Enisyl and Viralys are both good brands, and can be purchased over the counter without a prescription - just follow the dosing instructions on the label based on your cat's weight. If she's congested, you can also try using a humidifier or bringing her into the bathroom with the door closed while you take a hot shower - the steam and humidity help to break up congestion and temporarily relieve symptoms associated with respiratory infections.

Now if she does develop any of the signs I listed above, then I would be concerned about pneumonia, and in that case, I would take her into a vet right away. Best of luck, I hope this helps!