Vet call. At least call the surgery. Some will give free advice over the phone maybe? They do here in England. Keeping your cat hydrated is PARAMOUNT, just like Percival said. They are smaller, so they dehydrate a LOT faster than humans. I mean in minutes they can do so, dangerously... also make sure to clean up after them. Yeah you're gonna be doing that a lot.
She's probably crying because she feels unwell and is thirsty as hell.