Hello
These are often complicated issues involving multiple underlying things. To include diet, litter and litter box dislikes and environmental stress. I would look for a vet who specializes in feline medicine and place different kinds of litter boxes and litter types for your cat. Also make the area your cat lives in is as free of stress as possible. Calm quiet and easy to access all of the things she needs. Like fresh high quality canned food. Fresh water. And immaculately clean litter boxes. Also I add an anti inflammatory like dasaquin and a pain medication. I like gabapentin but your vet might use something else. Also ask about learning how to give sq fluids at home. Follow up with a urinalysis too.
Good luck
In a perfect world every pet would receive a second opinion. I think that is a great idea!