How can I hydrate my 6mnth old Beagle until tomorrow when I can take her back to the vet?

Bathing her will do absolutely nothing other than stressing an already sick puppy. Offer her low-sodium chicken broth. If she won't drink it willingly, use a turkey baster or enema bulb to squirt a teaspoon at a time into the back of her mouth - hold her mizzle and stick the nozzle in at the back of her jaw. Give her 10 seconds between doses.