does she have a cold or allergies? sometimes its hard to tell. Ours had allergies (we thoguht it was a cold). She is 16 m.o. and weights 25 lbs. Our doctor has us give her a 1/2 teaspoon of Zyrtec. But everyone differs, I woudl not take my advise or another mother's on here(regarding dosage), make sure it's a doctor. If you are unsatisfied with yoru doc's advise, get a second opinion. Try calling a nurse hotline, some insurance's have the phoen # on the card, and some cities have them too.
If her cough is hurting her, try a holding her in warm shower or take a humidifyer into the room she is in and spread vicks vapor rub in the tray in front of the nozzle (if it has a tray).
I hope she feels better soon!