This could be from parasites such as worms or coccidia or giardia.
It might be that you gave her a fatty treat that triggered the diarrhea.
It sounds like her anal area might be sore so gently washiing it off with a mild dog shampoo then applying some petroleum jelly to help with the soreness of any raw skin in that area.
You can give her plain pedialyte instead of water to help keep her hydrated.
You can swap her short term to a bland diet such as boiled chicken meat or hamburger with the fat drained off mixed with plain cooked white rice for her meals instead of dog food. You can add some cooked sweet potato or cooked carrots to that for fiber or some plain canned pumpkin to help with the diarrhea.
All this is 'first aid' type stuff to do but if she seems really sick and lethargic, or if you start seeing bloody diarrhea, or she won't eat or drink you should see the vet with her for immediate care.
You should probably have your vet check a stool sample Tuesday if she seems OK with just home care up until then.
Hope this helps you!
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