Hi Claire,
My understanding is that struvite crystals are quite common and a normal finding in dogs which do not require any specific treatment. They are a concern there is a history of sterile struvite stone formation. which is very rare. Most struvite stones form secondary to infection and my understanding is diet will not prevent urinary infection or stone formation secondary to infection.
“Struvite crystalluria occurs in greater than 50% of healthy dogs, including animals without urinary tract infections”https://www.dvm360.com/view/stones-vs-crystals-management-and-prevention-proceedings
Since leaking urine at night is a new sign consider checking for infection or presence of other contributing factors or causes.
I would consider SO to be a high quality nutritious food
