I am not sure what is wrong with your niece, but I am moving your topic over to the parenting forum. Maybe the girls over there will have some advice. I dont have anything other that to take her back to the hospital because there is obviously something wrong with her.

take her to a doctor (hospitals are notoious for the "its just the flu" responce) and DEMAND they either send her to specialists that will help or that they do tests. im my opinion she needs to see at least a gi for the vomiting and diarriah and a neurologist for the walking. she should probably get gi tests nurological test and if you ask me, metobolic/genetic tests. wqalking is a big thing and to loose that over night is a HUGE deal. my daughter has a suspected metobolic/mitochonderal disorder and she has many of the same symptoms. if you want further information on tests or specialists or my daughter pm me and we can talk easier that way (there are things i dont feel comfortable putting out on the public forums)

please do ANYTHING you can to get her parents to listen to you and get a second opinon, time very well could be of the essence and if something god forbid were to happen to her that would be a lot of guilt for her parents (and possibly you) to handle, its better to get things looked at and be told its nothing then to have something bad happen

:hug::hug:

Yesterday my 2 year old could not walk....so I took him to the Dr. and they said he must have pulled a mucsle, give him Motrin, and he should be okay. This morning he is crying and I don't know what to do, because the Motrin and warm baths are not working.