any OTC cough medicine you buy wont cure the cough. It may alleviate it for a few seconds but wont stop it - don't waste your money
Fluids, as much as you can get her to drink. Sucking something to keep saliva flowing could work as well
If it's that bad a trip to your GP to rule out any infection
I am suffering with a thick cough kindly donated whilst in hopital, so I boil a kettle and put in a tiny amount of Menthol Crystals with a towel over and inhale the fumes for ten minutes.
plenty of rest and liquids! drinking plenty is the key! water gets boring when your ill and you need a kick of energy so when im ill i drink water and sprite or lemonade :)