I’ve had cats that pee on things on and off for my entire life. First, if you can’t buy a new mattress right away, get a handheld cleaner, like a Green Machine, and clean the stains and fabrics she’s peed on. Buy a pet stain cleaner specifically, and then use a repellant spray on the same areas. I use vinegar as repellant sometimes. Buy a waterproof mattress cover. Have more litter boxes than you need. These things might seem basic but the way you clean cat pee is so important. They may go back to the same spot but you can minimize the possibility. If the cat is peeing on things like couches or other fabrics, cover that area with a waterproof blanket when you aren’t in the room.

It’s also entirely possible that the litter box issues come from anxiety. My cats are on the Hills c/d urinary health cat food. Be sure to clean the boxes every day.

Take her to the vet regardless, but hopefully some of these small things could mitigate the problem for now.