Yes, the Tylan50 is what you want. Dosage is .25ml per pound of weight given orally 3 times a day for 5 days. Can you weigh her? Got a kitchen scale or you can weigh yourself then pick her up and weigh again, that might get you close.
Tylan has a wide dosage range according to Plumb's Vet Drug Manual, dosing for birds is 10-40mg/kg give 2-3 times a day for 5 days. The dosage I gave you is "mid-range" so it would be hard to overdose her. Tylan50 is well tolerated in birds.
Bacterial respiratory disease like Mycoplasma responds fairly well to Tylan50 and other antibiotics. If it's viral like Infectious Bronchitis, then it will have to run it's course, but antibiotics can still sometimes offer supportive care and lessen secondary infection.
I would check her crop first thing in the morning to make sure it's
empty. Sometimes it's the angle of a photo, but her crop looks quite prominent. Has this girl ever laid eggs for you? How old is she supposed to be? I would also feel her abdomen for any bloat or feeling of fluid. Compare her to the others if you need to - cup your hand under her vent between the legs.
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