Will Falconer, DVM Moderator
Hi Sarah,
I'm so sorry your older cat has been through such stress. The propensity for making stones is a separate issue from protein content. There's something amiss in 1. diet composition and/or 2. the cat's metabolism that allows the formation of stones. As you've probably learned, this, like most chronic diseases, is a man made illness entirely. So, your next generation of cats will benefit from your experiences here, and likely be either raw fed or at least, healthy can plus amendments fed.
As to where her protein level should be, it more depends on how much kidney reserve she has left. The BUN gives us some idea of that. If it's over 80 and staying there for weeks, she'll probably benefit from staying on low protein diets. If it's under that and staying so, she could likely benefit from some more healthy raw protein and might even want to eat it, if it's made tempting enough.
I hope this helps. Getting off the kibble was probably the best step to keep crystals from returning, but it may not be the only necessary one.