As an alternative to euthanizing her (which I agree is really the only option if you are at the end of your rope and getting rid of her, one way or another, is the only option you seem to have left), would your hubby be willing to try confining her to an outdoor pen? If she had a large outdoor pen with a top and a secure shelter for when the weather is bad, then she would no longer have access to your belongings. She could spray in her pen without causing too much of a problem.
I know it's not the same, but for a while one of my cats refused to urinate in the litter box. It started originally as recurring bladder infections with crystals and then developed into a litter box aversion that was purely behavioral. We were about where you were now, he had ruined one too many of our things and we just couldn't allow it to continue. The vet put him on amitriptyline (which is a tricyclid antidepressant) and we confined him to a dog crate for about 2-3 months so that he had no option other than peeing on the towel lining the crate or the litter box in the crate. For a while we were washing out the crate daily because he still refused to use the litter box, but after a while he started using the box again. Finally we were able to wean him off the amitrityline and let him rejoin the household. Confining your cat to a pen may have the same effect in the long run of retraining her not to urinate in inappropriate places. Or it may not, but it could certainly buy your kids more time with a beloved pet and save your belongings at the same time.
The pen is a good suggestion, but our yard is really small, and we just put in the chicken run! This cat never had a problem using the litter box to urinate, so I don't know if your course of action with confining the animal would change anything. I will ask my vet about this as a possibility though!
Thanks for your input, I'm glad you were able to retrain your cat.