Maybe get that room cleaned (paint or shampoo carpets if you have to) and/or use some
Feliway, if indeed it is a territory thing.

Maybe she doesn't like her litter or litterbox. Try changing those - that worked like a dream for Sophie. We got her a covered box and all her accidents stopped.

Can you ban your kitty from that particular room - is there a door you could keep shut all the time?

Does she ever go in the box, or is it always on the wall? What about going #2, does she go in the box for that?

Sounds like you've been patient with her, and I commend you for that. Cat messes are definitely not fun. Please keep us updated on what you try, what works and what doesn't, etc.

Good Luck!