The most common cause of this is a parasite problem, giardia or coccidia. You need to go ahead and take a fecal sample to your vet's office and have it analyzed for parasites so that you can get an appropriate medication.
I would wager that this will help your problem.
Until you can get to the vet tomorrow, you can boil some chicken (no bones, no skin) for her and see if she will eat some white rice. Keep her hydrated by giving her plain pedialyte.
Then see the vet tomorrow for the fecal float.
Let me know if you still have questions.
