Now if we are seeing a sudden onset of sneezing fits with discharge from both nostrils, we do have a range of conditions within the airway to consider. In your lass's case, with the clear discharge from both nostrils, we can put worries of foreign bodies like grass or grass seeds lower on our list of concerns. This is because only the truly unlucky cat would end up with material caught in both nostrils. Furthermore, cats with foreign bodies caught in their noses tend to be constantly irritated and may rub their faces in between sneezing fits.
With this to the side, our most common culprits will be nasal based diseases like allergies and viral infection. These can all cause sneezing due to inflammation and nasal passage narrowing they induce. Lesser concerns for a cat her age would be growths (sinister ones and polyps) and potential nasal fungal infections.
In this situation, since her nasal discharge is clear (where snotty discharge would suggest bacterial infection requiring antibiotics from her vet), you can try some supportive care to see if you can reduce her signs for her. First, since sneezing is the body's way of trying to force congestion from the nostrils, you can consider taking her in the bathroom while you run a hot shower. The steam will help loosen and clear any of the snot congesting her. You can also use a baby nebulizer/humidifier, but often cats don’t like things held up to their faces. That said, you can alternatively make a little ‘steam tent’ with her in her carrier, the nebulizer, and a bed sheet over both.
Otherwise, if she is building up mucus that the steam isn't shifting, you can also use saline nasal drops (like Ocean Mist but not anything medicated) to relieve her congestion and help clear the upper airway. To do so, take one at a time and tilt their head back and drop two to three drops in one nostril. Cats hate this, but it helps. After the drops go down, you can let the head up and wipe away any discharge that gets loosened. Then repeat with the other nostril.
Further to all of this, if she has any history of viral respiratory tract infections and herpes is suspect, I would note that you can also consider trying her on L-lysine (a nutritional supplement) that can help cats with feline herpes virus recover from tracheitis quicker. It is available over the counter (at vets, health food stores, pet stores, etc) and tends to come as huge tablets that require crushing/mixing with food (since they are way too big to ask a cat to swallow). Usually we give an average cat dose of 500mg a day.
As well, to rule out allergies, you can also consider trying her with a short course of Benadryl (More Info/Dose). This is typically give at a low dose (ie. 0.25mg per pound of her body weight twice daily) and can reduce sneezing from airborne allergens. We like to keep the dose low in kitties, as they can have drowsiness with this medication (just like people). And of course, this medication shouldn't be used she has any pre-existing conditions or is on any other medication without speaking to your vet.
Overall, we can see sneezing fits in cats for a range of reasons. Since the discharge is clear and from both nostrils, bacterial infections warranting antibiotics and foriegn bodies being caught are less likely here. Therefore, I would advise the above approach for your lass. If you do so and she isn't settling within a few days, then we'd want to follow up with her vet to just rule out those less common concerns that could also induce sneezing. And if those are clear, then her vet can just dispense a kitty safe anti-inflammatory +/- decongestant (since human ones are not cat friendly) to clear this for her.
I hope this information is helpful.
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All the best,
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