Hi, I hope she is dewormed.
Second reason could be runny nose, that usually causes dripping of nasal secretion in throat when child sleeps, causing cough in lying down. Kindly use nasal saline drops every 4 hours in both nostrils, and make her sleep on one side right or left , and if no improvement pls revisit your doctor
"This provisional advice provided by me stands subject to the patient undergoing a physical examination and is based entirely on inputs provided by patient/attendants. The patient is advised for physical examination at earliest"