Hi Doctor, My Grand Daughter Has Been Off School For

Hi Doctor,
My grand daughter has been off school for a week, at first she was vomiting and had the runs now she has stiff joints in her legs and has difficulty walking. My daughter took her to the doctor who has prescribed panadol and neurofen she is no longer vomiting or has the runs just the stiff joints in her legs, what do you think is the cause or medication that could help her.
Thanks ...John Waring