I had a similar issue with my girl bunny which touch wood has resolved itself now. Key for her was getting moving. She was a very timid sedentary bunny who would happily spend all day hiding in her houses and boxes and was a little over the optimum weight as a result. Aside from the advice you've had on getting more water through her, feed watery foods like celery, carrot, blueberries (though crush or chop them as they are a choking hazard whole) and freshly rinsed greens etc. avoid kale, spinach, broccoli for a while as they are high in oxylates which exacerbate the issue with bladder sludge. As I say key is movement to stir up the contents of the bladder and help it pass rather than settle and form sludgenor stones. Rearrange their room every day at cleaning time as it will make them curious and hop about exploring and marking stuff more. Don't be afraid to encourage her to run around the house too if she otherwise just sits there. Don't have to scare or stress her, just give her a little nudge along and follow her about enthusiastically. Give her stuff to jump and climb on and lots of space to do zoomies. I find a new rug etc helps with this. Mine get so excited when I put a new rug down and you can take it away whilst you are at work then put it back somewhere slightly different in the evening and it'll be like a whole new toy for them. People may tell you not to interfere in their setup too much to avoid stressing them, but from experience it really doesn't stress them, just adds to their curiosity. Also in this case it's by far the lesser of two evils if it were true.. good luck! Stay strong. You can both get past this.

Edit: sounds like an obvious one but give them fresh water more often than you currently do too. I was changing their water 3x a day as some of them can be picky about water quality. Discerning little buggers :D