My 17-year-old female cat has had bloody stool twice in the last week
to week and a half. The second time I also saw mucus. (Unfortunately,
it was last night, so I couldn't take it to the vet in time for them to
detect anything.) She had a full physical in April and geriatric blood
work in June and passed with flying colors. In June she also had a
prolonged bout of diarrhea; no parasites were found in her stool and
the problem was finally alleviated with a sulfa medicine and a switch
to an "alternative protein" diet (Prairie then more recently Natural
Balance). She and the other cat both seem to have trouble eating the
canned food (they'd been exclusively on dry before)---as if they can't
figure out how to get it into their mouths. They lick it and end up
pushing it off the plate or plastering it to the sides of the bowl
(I've tried both types of dishes hoping one would work). I've also
tried breaking it into small bits so they can mouth it up and mixing it
with water to make it easier to lick up, with mixed results. She hasn't
been eating for the last few days; I think it's because they were out
of the Natural Balance and I got her Prairie again; my other cat also
won't eat it (although they both act hungry and ate scraps of fish from
our dinner a few days ago). She just scarfed down some canned pumpkin
so I know she's hungry---but not hungry enough to eat the canned cat
food?!? I hesitate to take her in again so soon as she was fine just a
few months ago and it's very expensive, but I'm worried. Is there
anything else I can do/try, or should I just take her in? Last time it
took weeks to cure the diarrhea after three medications, checking her
in for a few days so they could hydrate and observe, and the
aforementioned blood work; it cost a bundle and I can't keep using up
my savings indefinitely.

Thank you in advance for any suggestions you can give!