The problem you're getting into now is your bun is now a teenage bun and hormones are coming in. This can prompt territorial marking. If it's just happening occasionally, she may just be distracted from remembering where the litter box is because of her young age. If so, adding more litter boxes around the room could help fix the problem.
If she's just peeing in certain spots, you can try putting another litter box there to see if that clears up the problem. Otherwise you may just need to restrict her area to her smaller play yard and not allow free roam unless strictly supervised where you can scoot her to the litter box before a pee accident, or not allow free roam until spayed. There are also some tips for litter training, in the link below.
https://rabbitsindoors.weebly.com/litter-training.html