Hello, and thanks for writing in.
Yes, coconut water is safe in cats, so it should not pose a problem. Other things that may help with hydration would be to offer Pedialyte, generic pedialyte, beef broth, chicken broth, and tuna water. You can also give the liquids with a syringe or a turkey baster if she won't taken them in on her own. Canned cat food can also help, since it has a high moisture content. You can always blenderize canned cat food, or turkey, chicken, or fish, and mix water to make it like a soup, and then give it by mouth with a syringe or turkey baster.
I hope this helps. Please let me know if I can assist further.