Just to add a little bit more info as to why this could be a resistant infection vs allergies:
Infection: A couple days before this all started (Monday or Tuesday 02/28 or 03/01), I accidentally left the dust bath in her cage for 3 hours (I fell asleep). There was urine in the dust bath when I removed it from the cage. By Friday morning (03/04) I noticed she was sneezing a lot and had a nasal discharge/crust. I took her to the Emergency Vets that night and the vet on duty there put Linda on Baytril 1.00 cc, every 12 hours. Within the next couple of days, the quality and quantity of her droppings severely deteriorated to the point where she pretty much wasn’t going at all. So I took her to a different vet (who has worked with chinchillas in the past) on either Tuesday or Wednesday (03/08 or 03/09) and he had her stop the Baytril immediately and prescribed her a special probiotic gel/paste. By that time, here sinus symptoms were nearly gone (I heard here sneeze maybe twice a day, as opposed to several times an hour, no more nasal crust/discharge), so the vet suspected that the “overdose” of Baytril likely killed off her sinus infection since it also killed off everything in her gut. He said if it returned, to give him a call and he would further instruct me on a new dose of the Baytril that I already had.
Well, her droppings went back to normal right away, and some of her energy and appetite returned by the next day. But she never completely went back to her old self, and I noticed she was rubbing the side of her nose on rough surfaces a lot, like pumice and the corners of her platforms. And sure enough, by Sunday (03/13), her sinus problems were just as bad as they were originally, with frequent sneezing, discharge, and crust. So on Monday (03/14), I called the vet and he had me put her back on the Baytril at 0.25 cc every 12 hours. I had actually started her on it myself the Sunday night/Monday morning at 0.20 cc because I didn’t want to delay her treatment. When the vet gave me the new dose, he was concerned that she might have developed a resistance to it, and said if she wasn’t improved within 48 hours that I should call him and he will prescribe her a different antibiotic entirely. Well, she did seem slightly improved within those first 48 hours. I only heard her sneezing a couple times per day. So I kept her on it. But by Friday (03/18) she seemed at her worst once again, with the more frequent sneezing and nasal discharge/crust. I had gradually increased her dose up to 0.5 cc on my own but she’s still not improved. Luckily, her droppings have been ok for the most part since I put her back on the antibiotics, just a little on the small side. I have been giving her plenty of probiotics in between antibiotic doses. I will note that throughout this process, I have not seen her run in her wheel once and she seems to rest more than anything else. Also, while she does eat and drink enough on her own, her appetite is not what it used to be.
Allergies: Discharge seems to be clear (although it does form crust sometimes). Does not affect lungs (sinuses only). Allergy season/pollen has been particularly bad here recently. Windows are open in room where she is housed (temperature has been in the 70s F). Other pets (dog) has similar symptoms with clear nasal discharge and sneezing, and this was determined to be allergies. My main concern is that she’s never displayed symptoms of allergies before, and I have had her for over 13.5 years of her life. She has always lived in the same place too.