Zithro alone, excellent on rat under 12 months.
Baytril alone excellent for all ages.
Zithro and Baytril combo works every single time when trying to treat a persistent URI or when it's very advanced.
Could you bring her to Dr. Munn, she'd know what Starla needs. If she's been sick for a couple of months, she needs to be hit hard with the meds. And a vet that is not on the ball with rats, will not know to go strong with the meds.