You could give her a teaspoon or two two or three times daily by mouth if you prefer, but she should be able to drink it in her water. Pets seem to like water with CS added, and if you might note that the CS will help keep any pathogen contamination of the water at bay.
It could well be that the probiotics caused or contributed to the loose stools, but exactly why I am not sure. Possibly die-off due to bad bacteria being replaced by good, or maybe the product just did not agree with her?
Canned pumpkin (pure pumkin and not pumpkin pie mix) from the grocers shelves will usually help with diarrhea and cats generally love the taste.