What can be done to improve immunity in 4 years kid?

Hello doctor,

My daughter is 4 years and 2 months old. She develops a very bad cough and then along with fever in a day or two. She had a wheezing problem previously so the doctor had prescribed to give Budecort and Levolin puffs or nebulization. So every time when she develops this kind of a dry cough, I am not able to differentiate whether it is just a dry cough or wheezing related. Her cough kind of gets worse in two days and also while sleeping, she coughs continuously. My doctor has suggested giving Ascoril LS and if a cough does not subside then try giving Levolin. What medication should be followed? Also, Metal-P has to be given if the fever crosses 101 degrees Fahrenheit but my concern is which thermometer has to be followed. The touch thermometer or the digital one as both show different readings. She gets a fever every six months and we end up admitting her for high-grade fever. What should I do to improve her immunity? She has also started complaining of leg pain once in 2 or 3 months and I was told it is growth pain. Is it of any concern and is there anything that I can follow to prevent it?