I’m not sure that I’d give up on the vet route, but reducing dust inhalation or allergens can help (check her hay too – a switch from Timothy to Orchard might help). Also, feeding echinacea daily can boost her immune system. Most people don’t have access to fresh, so dried is great too – I used to take the contents of an organic echinacea tea bag, and mix them with a tiny bit of mushed banana and feed that way.

I have no experience with a nebuliser on my bun, but as an allergy and asthma sufferer, I have found relief from using a room humidifier on dry air days (so when air con is constantly running in midwinter or midsummer).

Based on my experience with Wick, I also recommend, if finances and rabbit-savvy vet allows it, to continue trying different antibiotics. I’m unsure how often your rabbit sneezes, but Wick had very frequent sneeze attacks and he couldn’t sleep very soundly, so it was important that we did our best to help him.

Start to finish, Wick’s upper respiratory infection took about 4 months to treat, of twice daily antibiotics. We started with one and it didn’t work, switched to another which sort of worked, then added shots on top of the “sort of” antibiotic and that was the right combo to attack the infection in Wick. Different antibiotics treat different bacteria, so it could be you haven’t found the one to do the trick yet. What medications have been tried, and for how long? Did any lessen symptoms at all?

Reduction of hay dust can help lessen nasal irritation. I switched from Kaytee to Oxbow brand, and it made a large difference as well. If you use a dusty litter, you can put a litter screen down to help quell the dust pick-up as well.

I had a bunny on a nebulizer, they are very helpful for rabbits with breathing difficulty, I would often just use nebulizing fluid (which is distilled water with no impurities in it) to help

We also used it to get certain antibiotics into his lungs directly. Do be sure to talk to the vet about the partical size needed-its smaller than the ones used for babies and is somewhat specialized.
Im with wick though -try a new antibiotic to see if it will help clear it