13yr old cat chronic diahrrea, I can't lose another one!!!

My dear Sissy cat and I have moved alot in the past few years, but I have just
moved to Tx from Wa and now she has diahrrea all the time. I don't know if it
is the water which I think stinks, but my mother doesn't, who has lived here
for 15 yrs. I have also turned her into an indoor cat from an outdoor cat.
There are too many predators around here to get her. I already lost a cat like
her years ago when I moved down here then. I also feed her an indoor dry food
formula and a hairball dry food formula as well as canned cat food. Could
someone please help me. I am on SS disability and can't afford a lot of vet
bills at this time. My mother is retired and widowed. She eats alot and all
the time, and seems to drink enough water although I don't see her drink often
enough. We have been here almost 2 yrs. now so I don't think it is stress. She
seems very happy and loves her dried catnip. She hates not going outside of
course. Thanks for any help please.