Oh no Luna, not again, poor girl

Kirsten, you've probably posted this somewhere else but I don't remember: is Luna on a very specific diet for cats with urinary infections? We had a cat at the shelter who was very sensitive to UTI because he was not drinking (not at all!). He had only one sort of wet food that we mixed with water. One day a volunteer made a mistake and gave him another food. The amount was really nothing but the day after he was sick. This is an extreme case, but I was wondering to what extend another food would delay the relapse for Luna.