Can you telll us what symptoms you are seeing? Are there bubbles or foam in either eye, mucus from the beak or nostrils, swelling around the eye or face, sneeze or cough? Is there any bad odor? How does her crop feel? Have you added any new birds recently? Few antibiotics are approved for chickens. One that is, is Tylosin powder to use in the water. It treats mycoplasma (MG) a chronic respiratory disease. Denagard or Tiagard is another drug used. Other antibiotics such as oxytetracycline, doxycycline, or sulfa antibiotics can be used with an egg withdrawal time. Vets are prohibited from prescribing Baytril (enrofloxacin) since it is against FDA regs, although some use it with a ling egg withdrawal time. If the chicken has a virus, then antibiotics don’t help unless there is a secondary bacterial infection. I would get the Tylosin and give it in the water 1 tsp per gallon of water for 5 days only to her.