If it keeps her up tonight, try cough drops and hot water with lemon and honey to make her stop coughing. Also let her sleep in a recliner or propped up on several pillows. If she finds something that makes her stop coughing, don't make her get up and brush her teeth. It's gross, but her teeth won't rot out over night, and brushing her teeth might be enough to tickle her throat and start the whole thing over.
I would only treat symptoms that are making her simply too miserable to get to sleep. Coughing and sneezing and even running a slight fever are ways that the body heals itself.