Dog is wobbling and a little unresponsive - 5 month old puppy?

My 5 month old beagle mix spent the afternoon at the lake with my husband. They came home and she's wobbling, unresponsive for the most part (won't pay any attention if you say her name or call her or say anything to her) and threw up (brown, very liquid, a little gr mixed in). She didn't have any food while she was at the lake and only drank the lake water. So, I'm not sure if there was something in the water or if she got into something else or if she's just dehydrated/super hungry. I talked to the emergency vet and she said it was probably something in the water and up to us if we want to bring her in. Just not sure if that's necessary are not. Help!