She has rales and is shaking her head often, swallowing mucus drainage. Does she or has she had any bubbles or sticky drainage in either eye, or swelling on her face or eyelids? Have any others ever had any symptoms in the last 2 months? She obviously has some chronic respiratory disease. Common ones are MG, coryza, ILT, infectious bronchitis, and a few others. Some are viruses, some are bacterial, and mold fungus can also cause symptoms. Tylan 50 dosage is 1.25 ml for a 5 pound chicken given 3 times a day for 5 days. Tylosin powder, the generic form that is put in the water (1 tsp per gallon of water for 5 days,) is available online from Jedds.com and birdpalproducts.com. If she has a virus (IB or ILT,) then it usually takes a month or so for symptoms to run its course, and antibiotics don’t help unless they get a secondary bacterial infection. The best way to know what she has had, is to have your state vet do a necropsy on her if you lose or decide to cull her. Here is a list of state vet vets including TX:
https://www.metzerfarms.com/poultry...7IOlHOhP-eD8qMtZ70RNq6BMO9kVUn3x6so7q0Z_JgEr8