My Granddaughter (7) Has Been Sick The Past Couple Weeks.

My granddaughter (7) has been sick the past couple weeks. She has bee running a spiking temp of 103+, has headaches and a tight neck and sore through. Her mother has taken her to Emergicare, ER, and the pediatrician. The pediatrician said she and her 5 yr old brother had hand-foot-mouth, but it does not explain the temp. ER and Emergicare just said it was a virus and give pain releavers. Could it be something more serious than hand-foot-mouth?