I would take her back to the Drs or give the hospital a call. If she isn't keeping anything down she needs to be seen,,

This time last year we had a terrible gastro bug go through the house. My 8 yr old lost heaps of weight . We managed to get Jelly into him by using a syringe and telling him it was medicine from the Dr and he managed to keep that down. ( he was 7 at the time) Our 4 ( 3 at the time) yr old ended up in hospital for 5 hours being monitored. They didn't do a IV because thankfully after 5 hours of sipping water and keeping it down he peed.

I hope your DD gets well soon.. and that no one else gets it