You're sure they were cystine stones? Those are really rare and diet doesn't seem to help prevent more crystals from forming. The jury is split 50/50 on diet. Some vets say low protein since meat causes the body's acidity level to rise, some vets say it doesn't make a damned bit of difference either way. Since there is no definitive science either way (low protein v high protein) I'd need to know what SHE is comfortable feeding.
There are groups that she can join, I learned about them during all my kidney research. I can send you a couple if you want to pass them along.
I can definitely tell you this tho, if it is cystine he can't have any poultry products of any kind. EVER!