If she is on an antibiotic, she's already seen a doctor. What did he say?
Another thought is asthma. She really should go to the doctor and get a full check up.
Possibly sleep apnea. It is a difficulty breathing whilst asleep which leads to anxiety and waking up gasping for air.
It is caused by the build up of carbon dioxide in the blood stream which stimulate chemo receptors, these are neurons which detect specialist chemicals in the body.
Although, this is only one option.