Hopefully your grand baby is ok! Definitely a Dr is needed! My Step daughter started seizing after a high fever when she was two also. The ER said it was not uncommon for children and usually stops by age 5. Thankfully she had only the one.
She need to be seen by a Dr. ASAP. I'm an EMT, it could be anything from febrile seizure, to issues with her kidneys.
It siunds like she has or is having seizures. Take her to a doctor asap to be certain. I hope she will be okay, best wishes
Contact her pediatrician immediately! It could be a seizure. If they are closed, I would even go so far as going to urgent care.