i have to disagree with your vet.. i would NOT withold water no matter what... I would try feeding her.. if she throws it up.. then yes i would withold food until tomorrow. but i would keep encouraging her to drink water.. you do NOT want her to get dehydrated. Tomorrow i would try feeding her again... if she still throws it up i would boil chicken breasts and white rice and feed her that until she is able to keep something down. I would also try givng her some pro biotic yogurt to help get back the good bacteria in her tummy that she needs. Don't worry (i know.. easier said than done) it's very scary.. especially when it is the first time she has been sick... but we've all been there
let me know if you have any more questions and try feeding her to see if it will stay down.