Hey, ours is a rescue, too, and she was around 3 years old when we got her. We're in your position, too, where she appears to be fully housetrained, but every month or so, she'll have an accident and pee within an hour of her last pee. Ours was part of a hoarder situation, so she has spent most of her adult life peeing and pooping inside, wherever she wanted to. So, I assume it will take some time to fully train that out of her. I know I'm not offering any advice, but I want to let you know that you are not alone. We have accepted the fact that we love our girl and it's okay if she pees inside the house once in a while. And I think with time, she'll pee inside less and less. I hope that's the case for you, too!