My cats preferred the rabbit over the duck...and they like the lamb too. Can she have lamb?

Royal Canin just joined with Waltham to formulate a new Prescription Food line. Maybe you can ask your vet about that?
http://www.walthamusa.com/Learning%20Center/RD30.html

Micah has IBD too and does pretty well on the IVD/Royal Canin/Innova mixture. Our vet is also watching his kidney function because of his last test results. We didn't have any luck on any Hills product, in fact, they made him worse.