The vet recently put my cat Rusty on Hill's prescription canned I/D for his
diarrhea. So far so good.

Winnie

The first thing my vet tries for diarheea is no dry food. I also hear that
silver bark may help.

One of my cats had IBD (along with progressive kidney/renal failure).  This
was a number of years ago, and I didn't know about Wellness then (although
it is the food I now use), so I can't address the question about IBD and
Wellness.  However, you mentioned diarrhea.  Amber had continuous,
incredibly severe diarrhea along with her other problems.  She was on a
regimen of Prednisone (gradually increasing, then a plateau, then gradually
decrease).  The thing that was most helpful in treating the diarrhea was
Imodium AD.  Amber was a very small cat, and the vet showed me the amount to
use -- I would use a very sharp knife to shave down the already-small
Imodium tablets into BB-sized pellets.  I eventually got good enough at it
that I got several "pellets" out of a single Imodium tablet.  I found this
to be very effective and much easier to administer than liquids.  The foster
mom should check with her vet first, but this might be useful in controlling
the chronic diarrhea.  Of course, that doesn't get at the *cause* of the
problem -- but at least it helps with the consequences of it.

MaryL