Yes I would take her back to the ER for sure! They can put fluids under her skin and that can help hydrate her! They could put her on an IV too. I would think she needs to be eating...perhaps syringe even.
I googled and found metoclopramide - Potential side effects of metoclopramide include diarrhea, fatigue, and frequent urination.
Did they test for Giardia and coccidia?