You should have your vet check a stool sample to see if the problem is parasites of some kind such as worms or coccidia or giardia.
If your dog is a puppy and has not completed its puppy shots this could be parvo and if it is that then ask your vet about treatment using the human medication Tamiflu. You can read about that here
www.marvistavet.com/html/body_oseltamivir.html
Another possibility is that she swallowed a non food item that is impacting her intestinal tract. Socks, string, toys, rocks, coins etc can all cause serious gastric distress and an x-ray of the dog might point you to the problem if its not parasites or a viral or bacterial disease.
A bloody stool means you should have the vet see her.
Hope this helps you!

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