As long as she is drinking water, she will not be easily getting dehydrated, but it is also what could be indirectly causing her to vomit more. But, you must get her into a cool area, and make sure she is not outside, especially with the heat the way it is. Try to pet her and comfort her, and if you possibly have some way to take her temperature rectally, you might have some one help you with that. A normal temp for a cat is about 101 to 101.5 (Please check out the following website):
Is she spayed? There is always the possibility of symptoms such as these, when a cat is pregnant. Unless you know she is spayed and has not been around any un-neutered male cats.
If you have a number for your vet that lets you leave a message, call them tonight, and let them know that you need to have her seen as soon as possible in the morning. If she seems to get much worse, you may have to take her to an emergency vet during the night. I am looking at the clock and it is almost one am now.
She may just have a virus, or it could be a number of things, causing her symptoms. Her age, and if she has any other health issues that you can tell us about.
Is she urinating okay? There is always the possibility of a urinary tract infection. Does she have her shots?
Let us know if you can, her age, and when this all began.
God bless and good luck!