Your other option is an oral antibiotic if you would rather not use the eye antibiotic.
You can also ask a vet to take a swab of her throat secretions and run a pathology test to see what bacteria is present. It can run into $$.
What we do here, unless it's something very obvious, is to suggest treatment for the most likely possibility and see what happens. $25 for some amoxycillin is a fraction of what a vet and testing would cost.
https://www.kvsupply.com/item/aqua-mox-250mg-capsules-100-count/P06184/