I'm so sorry to hear about Luna! Everyone has given you excellent advice and I hope it will help you. The Nature's Miracle is an excellent product. Here's a link:

Nature's Miracle

As everyone said, first find out if it is medically related. From my research on struvite crystals, it is recommended that cats who have continuing problems should be fed a high meat diet. Do you feed her strictly dried or mixed can and dry food? Maybe you might want to consider a raw diet, since meat protein is shown to be a natural urine acidifier. You might want to talk to your vet about this. Or you can look into providing an all meat canned diet that is available in pet stores.

If this problem is not medically related, you might want to talk to your vet about putting Luna on a low dose behavioural drugs to combat Luna's stress at certain times. Also a Feliway plug in wouldn't be a bad idea either to help calm Luna's nerves.

Best wishes going your way.