Thanks for posting your query.
I am Dr.Ratnakar and I am pleased to assist you.
No dry mouth
are not side effects of gentamicin
She is probably having diarrhea due to some reason and the dry mouth is due to dehydration
as a result of diarrhea.
Give her enough fluids, electrolyte solution to keep her well hydrated.
If the diarrhea is persistent, get a stool analysis done.
I hope that answers your question.