Oscar had this same kind of UTI - the cause was stress (Cole had arrived in my household lately). There were hardly any crystals, but blood in his urine! We got him cleared up and he was on a Feliway collar for a long time. I made one from a regular stretchy collar and would gently squirt Feliway into it twice a day.

It's been a few years now and all three are well without the collars or Feliway.

I am glad Lily will be with you for a long time yet!