Agree with ginger, totally! Can you go to another Vet?
I am so sorry she is sick like this.
What are they doing -sending her home, when she cannot even hold water down? How is she meant to hold down her medicines? (Unless the shots they gave her before she was sent home are meant to last?) But usually anti-nausea drugs have to be given maybe every 8 hours? Or something similar....
And it is obvious she will get dehydrated in one day in that position.
It is not your fault, but I question the vet's judgment.
A dog in that situation needs to be on intravenous fluids, and the ultrasound performed -sort of now!
What is wrong with her....obviously I can't say. But she is in a miserable position if she can't keep water down. She needs to be hospitalised in my opinion until she is stabilised, stressful though that will be for her and you.