Thanks for your reply.
You have not mentioned the name of the nasal drops.
Fenistil contains antiallergic medicine Dimethindene and can be given for allergic cold
after geting her examined by her Paediatrician.
Normal saline nasal drops can be used as they are safer to use.
At the age of 4 months, you can increase her immunity by getting her properly vaccinated and giving her proper feeds. Immunity will increase with her age.
I hope this is helpful to you.