She could have something stuck in her throat, or she may have a respiratory infection. Those can be viruses, such as infectious bronchitis, mycoplasma (MG,) or others. Look into her throat for any yellow patches or gunk that could be infection. What antibiotic did you find, since most are by vet prescription only? Tylan 50 injectable can be given as a shot or orally. I would use 1ml for every 5 pounds 2-3 times a day for 5 days. Syringes(3ml) and 20 gauge needles are needed to get the medicine out of the bottle. Unless you are seeing a lot of eye or nasal drainage, or facial swelling, my guess is that it may be IB. Infectious bronchitis will hang around for around a month with sneezing being the most common symptom.