If she habitually poops/pees in that one corner already I’m not sure there’s much you can do except clean the spot well (get rid of scent with vinegar + water) and block it off for a bit, and hope that after enough time she’ll forget. However there’s no guarantee that that would work, and it sounds to me like the easiest thing to do is to just add another litter box in that corner. Is it the room her cage is in? Most free roaming bunnies work best with multiple litter boxes in different rooms. Even if it’s in the same room, it’s not too unusual either to add a second one…a lot of the time, litter training a rabbit isn’t so much making them learn where to do their business as much as it is putting the litter boxes where they decide. It’s us getting trained, not them lol!
Also, if her litter habits are getting messier, it might be time to look into getting her spayed..she’s just about the right age.