She needs 50 mg pound per day of Tylan. You could mix it stronger just for her, say 1 tsp per liter waterer, and make sure that she drinks it. Or get the Tylan 50 and give her 1/4 ml 3 times a day. I am just saying, she may have something more hard to treat than the others that might require a different antibiotic. E. Coli and pseudomonas are other bacteria that can cause eye and sinus infection. Here is a link about Tylan dosage:
https://www.backyardchickens.com/threads/tylan-powder-help-and-dosage.1245955/
https://www.backyardchickens.com/threads/tylan-powder-help-and-dosage.1245955/