Wow, she is a pretty big cat for only being 10 months, but in this situation that is to her advantage. She could have an intestinal infection that could be either viral or bacterial. She could also have intestinal parasites. Has she had any diarrhea? If she has only not been eating at all today, that isn't critical yet, but if she vomits from drinking water consistently, then she could dehydrate rather quickly. In any case, I would take her to a vet in the next day or two if any of these symptoms continue. If it is either a bacterial infection or parasites, she will need meds to cure those. Even if it is a viral infection, if she continues to vomit even just drinking water, then she will need subcutanious fluids.
Yes, this is an emergency! Kitties can not go without eating for long before their organs begin to shut down so yes, an IV and tests are needed. Please don't delay especially since she's vomiting her water and is without a doubt, dehydrated.
Good luck and please let us know how she is!