Hello & welcome to Just Answer/Pearl. I am Dr. B, a licensed veterinarian and I would like to help you with your wee one today.
In this situation, with Emma's recent rehoming from a rescue, I would be very suspicious that she is having a flare-up of one of the 'cat flu' agents. My primary suspicion would be the feline herpes virus, though we could see a similar issue with feline calivirus or chlamydophilia felis.
Often we will see cats pick these infectious agents up in rescue catteries and shelters. This is because these are often places where there are a lot of cats under stress that are sharing an airspace. Therefore, it is the prime environment for these airborne infectious agents to infect all in contact cats. Now it is not surprising to hear that she didn't have any signs until you brought her home. And this is often the case. The reason is because often these cats will remain free of symptoms until they are under enough stress for the virus to overtake the immune system. And often the stress of a new place, new people, and new life can be enough to cause a flare-up.
In this situation, the Convenia may be helpful if there was a snotty discoloration ( a sign of secondary bacteria) of any of the eye/nasal discharges she may have had. In regards XXXXX XXXXX Maxitrol, I would consider halting it at this point. It is very good at taking inflammation down in sore eyes but it can be counterproductive with conjunctivitis that is caused by a cat flu agent (since the steroids would dampen immune response and potentially give the virus the upperhand). Therefore, if the eye is looking worse and she is now showing respiratory signs (which leads away from a primary eye condition that your vet likely suspected), then you might consider discontinuing the treatment and perhaps ringing the vet to discuss alternatives (ie antibiotic eye ointment if the discharge was snotty and suggestive of a bacterial component. Or Aueromycin eye cream if C. felis is suspect).
Otherwise, supportive care measures are often our mainstay of treatment and worth starting for her here. If she is sneezing and congested you can take her in the bathroom while you run a hot shower. The steam will help loosen and clear some of the snot congesting her. You can also use a baby nebulizer, but often cats don't like things held up to their faces. That said, you can alternatively make little ‘steam tents' with the kitty in their carrier and the nebulizer under a thin bed sheet.
If she is building up mucus that the steam isn't shifting, use a cotton ball moistened with warm water to wipe away crust and mucus. Use saline nasal drops (like Ocean Mist) but not anything medicated. Tilt the 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.
Making sure she is getting food and water is important, as congested cats who can't smell their food often won't eat as well as they should. Therefore, if she has had any loss of normal of appetite, then do consider tempting her with smelly wet foods (since they are high in water). It may help to warm it up a bit in the microwave to help her be able to smell it.
And since feline herpes virus may be a cause here, then we sometimes find the L-lysine (a nutritional supplement) can help them recover quicker. This is available over the counter at your vets or even some health food stores (and GNC type stores). They tend to come as huge tablets, so I advise crushing them and mixing it with food. An average cat dose is 500mg a day.
Overall, I would be highly suspicious with Emma's history and signs that she has contracted a cat flu agent. Therefore, consider stopping the Maxitrol and try the above to help give her some relief. As well, consider speaking to your vet about an alternative eye treatment or flushing/cleaning the eyes with saline (ie contact lens solution). Furthermore, if she is now very congested, they can prescribe cat safe decongestants (since human ones are toxic for kitties) like Bisolvin to ease her breathing.
Finally, if you try the above and feel she is worsening, then you may also want to consider testing/confirming which agent is present to allow you to target treatment and clear this for her. (This may be something that the rescue would help you with if necessary).
I hope this information is helpful. Please do let me know if you have any further questions.If you have no further questions, feedback is always appreciated.
All the best,
Please remember to only rate my answer when you are satisfied. IF you have any lingering questions or concerns, please stop and reply to me via the REPLY or CONTINUE CONVERSATION button with the issue you have. I will be happy to continue further and do everything I can to provide you with the service you seek. If you are satisfied, please click the 4-5 stars or associated happy face so that I may receive credit for my assistance.