Sudoku, I think you gave good advice. All the things you mention could be of help. It won’t hurt to try and encourage her and make it easier for her to get her good litterbox habits back. Serving hay within reach from the litterbox can really encourage a bun to do their business in the box, I see that with my bun Vilde who wasn’t fully littertrained when I got him.
I did notice with my bun Bam that when he had a bit of gas/ a tummy upset (he was prone to intermittent soft cecotropes), he could pee outside of the box. It didn’t happen often, and it always resolved itself when his tummy was back in shape again.
So this could perhaps be due to discomfort from the eye ulcer, or something else could be going on. Rabbits are so good at hiding pain and illness that us hooms must be super-observant.
Bh90, if your bun has been to the vet several times for the eye ulcer, they must know her pretty well. I think you could call them with your concerns. It could be about something as trivial as inadequate pain relief.
Iwould also start to weigh her regularly and write down her weight. Unexplained weight loss can be an important clue to a bun’s health and because of the natural fluffiness of a rabbit, weight loss is not easy to see with the naked eye unless it’s dramatic. I weigh my bun once a week in a bowl on normal digital kitchen scales and write his weight in my wall calendar.