Hi Kit E Kat,
While my advice is no substitute for that of a vet (even though vets will tell you to keep them on rX food for liability reasons), I have some experience with struvite kitties, both male and female. It really depends on gender, breed, and how far you are willing to go to reduce any chance of relapse. I'll try to find the %'s, but if I remember correctly you want to stay away from any salts, magnesium, and phosphorus, with a high % of moisture, to reduce stone formation.
Was the stone type confirmed with analysis?
One of my girls was recently diagnosed with struvite stones severe enough that she required emergency surgery to clear the stones and repair her bladder. She was on death's door by the time she let mommy know something was wrong. I dare not switch her to anything except an rX food for quite awhile. She did not have ANY UTI. Stone analysis 100% struvite. She was such an unusual case (female, rapid onset of symptoms, no infection) that I suspect a genetic susceptibility to stone formation. Kind of like some humans are more likely to develop stones than others. She has been on Purina UR, Hills SD c/D, and Royal Canin SO. The Purina is my preferred food, she isn't picky. The smell of the c/D literally makes me sick so I avoid it.
My mothers cat, a male siamese, one of the more common cases of struvite stones, was dX'd over 10 years ago, and has been off of rX food for the past 4 years based on my research and advice to my mother with no relapses. He did have a severe UTI when he was dX'd. He is on Authority wet NO fish formulas x2 and schedule fed Blue Wilderness (again no fish) around noon if I'm remembering correctly. I'll double check with my mommy.
Steer clear of dry food, fishy food especially in my experience. I give fishy anything ONLY when they are sick and it's the only way I can get them to eat. Avoid free feeding if you can help it because it will give you better control over fluid intake. I'll often moisten dry food in small batches and warm it up to make it more interesting and ensure that there is enough liquid.
As a 'person' that gets stones, hydration is KEY. (Although I get oxalate stones, I understand struvite is unusual in humans where there is no history of infection) The more you wee, the more you flush stuff out of your system that may develop stones. I understand that's part of how the rX foods work, not only by modifying pH, but also by encouraging more fluid intake.
Hope this helps!