Thanks for writing your query.
in short duratins can be either due to allergy
or due to the reason that the previous infection was not completely cured, which may be due to less senstivity of the antibiotic given to the infection.
It will be advisable that you should get her investigated for :-
1. Throat swab culture
2. Complete Blood Count
3. Culture and Senstivity of the sputum, if she can cough out the sputum because children are not able to cough out, they usually swallow the sputum
She can be given appropiate antibiotic according to the culture and senstivity report.
Give her antiallergy medicine after consulting her Paediatrician.
Other useful habits to prevent recurring infections are :-
1.Washing of hands before and after meals, as this prevents a lot of infections from entering our body.
2. Drinking pure filtered water.
3. Eating fresh fruits andvegetables.
4. Regular exercise in fresh air.
I hope this is helpful to you.