What to do about the diarrhea I really hope the vet knows.
But if she is diarrheing much, she has a lot of water losses.
If she drinks extra water herself to compensate, is good. Otherwise you must give her extra water by force if need be.
Only water will dilute her salt-balance. No good...
There is surely a commercial water-salt solutions, Pedialyte I believe it is called in USA. You can surely buy it in drugstore (Apotheke).
Otherwise you can make a basic but useful home pedialyte:
The dosage is: 1 tea spoon kitchensalt, 1 soupspoon dextrose (="grape-sugar") in 1 liter of water. Boil up, cool down to drinking temp.
It can be done more fancy, but this is the basic receipt. It helps with the salt-balance and is in some degree also stopper for the diarrheas.
This home-pedialyte does marvels in turning down the death-rates in kolera. From perhaps 70% into perhaps 5%.... (I dont know the exact procents, but know the numbers fall dramatically)
So. Do give her this pedialyte while you wait for the vet appointment. When with the vet, you can ask if there are other useful ingredients he wants you to add.