My mother experienced explosive diarrhea after getting a flu shot. Should she go to the ER?

I took your advice, called her doctor, I'm actually her health care proxy. The doctor then called my mother, and called me back. They told my mother to call 911 is she starts to feel dizzy, as this can be a sign on dehydration. And asked her to come in first thing tomorrow morning.

Can you call her doctor's office and discuss this? Or a nurse triage help line? If they recommend an ER, that is what you should do. Perhaps the doctor would like to see her in the office.