Chronic GI Issues

My girl has had chronic GI issues as long as we’ve had her (she’ll be 3 in November). It’s to the point we were going to the vet every other month or so spending hundreds of dollars but no long term treatment. We recently switched her to a new vet, and after another bad episode and all kinds of blood tests and X-rays to make sure it wasn’t a blockage, the vet suggested putting her on a hydrolyzed diet. We got some of the Purina Pro HA food and she hated it. So we switched to Royal Canin HA, but it’s still a fight to get her to eat. She’ll go a few days just eating some here and there and then I guess get hungry enough to eat her whole meal. Now she’s having diarrhea again, which I think has more to do with her no eating regularly than anything else, but does anyone have tips on how they got their basset to eat food they weren’t interested in? She’s never really been food motivated so much as treat motivated.