It could be allergic rhinitis. Also we need to check if she has adenoids or ear infection or allergy to any household or at school items. Recently did u change anything at home? Like curtains/ washing powder for her clothes?
Next Steps
since its there for now 18 days, so giving simply medicines should not be done. so you need to consult a pediatrician near by and examined her.
Health Tips
try to find if she has allergy to anything if u can.