Not much you can do if it's cancer, but if it's something like worms, coccidia, bacteria or yeast, you can treat those. If she were mine I would worm with Safeguard at 0.23ml per pound for five days, this will treat almost all possible worms (the one day dose you gave her probably just treated roundworms).
Any chance you can take a poo sample to the vet and have it checked for coccidia, worm eggs, bacteria and yeast? You should also look up ascites and EYP, see if those symptoms fit.
-Kathy