Diarrhea and then constipation?

Some of you may remember that my mom's 8 yo female longhair had a sore
on her right hind leg. Several months ago, after changing a hard food
formulation food too quickly she developed diarrhea which solved itself
in about two weeks.

Well, it's now about three months later and I'm not sure whether it was
the shot of depo medrol, the removal of an old carpet or getting her off
of Fancy Feast wet canned food, but the sore seems to have disappeared.

The problem is that after a week of another bout with diarrhea, she seems
to be constipated. My mom has this habit of giving the cat different
protein sources every time she meows. Instead of sticking to Iams Lamb
and rice (which the poor thing doesn't seem to like anyway), and Purina
Pro Plan Chicken and Rice hard food (which she does like), she was
alternating with chicken baby food, turkey breast, and cooked chicken
along with the normal hard food. For four days last week, the cat had
diarrhea. For the last three or four days she hasn't passed a stool.
She urinates with no problem, drinks, plays, and nibbles at her hard
food. She doesn't strain as she doesn't seem to have any desire yet to
pass a stool.

Should we give it another day? Should we go back to Fancy Feast even
though we're not sure if she has skin allergies to it? We've tried
Wellness, Iams, and IVD allergy brand food, and she doesn't like them at
all.

I've read in some places where baby food squash is helpful as is
Metamucil, but other sites seem to indicate that MORE fiber in the diet
could also cause problems.