I deeply sympathize since Sammy, 5 years old, has been peeing outside of her litter pan, too. I mean, right next to it.
The first problem is that once they put their smell there, they return to it. So, you are right about the vinegar wash, and you need to spray your couch with a 50/50 mix of white vinegar and water (after cleaning it with the vinegar, of course.) Spray the bottom of the couch as well, and don’t wash it off. Believe it or not, you won’t smell it after a very short time, but it will be bad to her, and it may be just deterrent enough to make her think twice.
Next, try a second litter pan near there, such as on the floor tucked away beside the couch. If you don’t mind a new pan being out all the time, it gives her a second option when she doesn’t feel like going all the way to her main pan. I had an “outside” pan in my apt. for Spockie, and a main one in his cage. So his away time from his habitat was easy for him to be clean. It worked for him.
To entice her to it, hide a couple of treats, or just some pellets, in the litter for her to smell, dig up and find. Whenever she uses the new pan, praise her loudly. (Good girl! Good bunny!) If you want, if she goes into it, give her a pellet or a treat immediately each time for the first week or more. You are training her with positive reinforcement to use it. If she pees on the couch, clean with vinegar again and don’t say anything. Negatives don’t really work on bunnies. But if you do see that butt wiggle, tail go up, or she hunches like she’s considering it, scoop her up and put her in the new pan asap. Then praise her.
After a short time, don’t make the treat every single time, so she is never sure if that’s the time she’ll get one. That way, they do the good thing in the hope that maybe they’ll get a treat. Then give her one on occasion for another week. If all this works, you should be back to normal by then.
And yes, bunnies hold grudges. They don’t like different detergents. They get mad and pout. Shame on you, Slave!