I am very sorry to hear that California is experiencing these problems, I am sure it is very unsettling for you both. There are a number of potential causes of watery stool, including dietary indiscretion, pancreatitis, parasite infestation, infection, and ingestion of a toxin or poison.
Because you have only noticed one watery stool I would continue to monitor California at home. Here is what you can do;
Rest Her gastrointestinal tract by holding back food for a few hours. Then you can continue with a bland and easily digested food of the boiled chicken breast and white rice diet and provide plenty of fresh water. I also find that boiled, mashed skinless sweet potato is helpful for diarrhoea, and preferable to banana.
If California does not improve, has profuse vomiting or diarrhoea, you notice fresh blood, She seems lethargic, in pain or depressed I would advise a trip to the veterinarian.
Here are some links to helpful resources for you;
https://www.petcoach.co/article/most-common-causes-of-diarrhea-in-dogs/https://www.petcoach.co/article/6-things-you-can-do-at-home-if-your-pet-has-diarrhea/I hope that answer was helpful and more importantly that California feels better soon. Warmest regards to you both.