Feeding cat new food for IBS

Question
My Vet wants my cat on a different diet for IBS, Duck and Pea Science Diet.  She is eating the dry version and initially ate the wet version mixeed with her old food over a 7 day period.  Now she doesn't want to eat the wet version at all. She has lost so much weight due to the IBS that I am worried she won't eat enough of the dry to start gaining weight back.  My cat stills wants her old moist food, she knows that I feed it to my other cat separately. Is it safe to assume that she will start eating it if that's all I will give her?  Thank you

Answer
I wouldn't tempt fate by giving her the old food. You could ask the vet if canned w/d would be safe as it is used for cats with colitis. If she needs a bland easily digested diet then the canned I/D for cats will work.
One of the reasons that cats stop eating one kind of food is because Science diet really fills their nutrition needs with less food, so the dry is probably filling that bill.

Wet food has more water than dry but that doesn't mean it will make her gain more weight. Fat content will help with that, not water.

But if you give her the old food you run the risk of starting up her IBS symptoms even worse.
So ask about the W/d or I/D and see how she does on those.