My cat was shaken by a friends dog last night. We brought her to Emergency Vet and they said she was OK. She won't eat or drink today and growls if y

When you took her to the vet did they do x-rays? What tests did they do to make sure she was okay?

Watch her for now. She had a traumatic event yesterday, is likely sore and a bit out of sorts. Not eating is a concern, but not drinking is really the thing you should be more concerned about.

If she hasn't started drinking by tomorrow than go to your regular vet.