Your rabbit may not want to eat that hay because there's something wrong with it, like it has mold or maybe was sprayed with something in the field prior to harvest that is making it taste wrong to her. I would check the hay to make sure there are no white or black spots in it, that it's not damp at all, and that it doesn't smell sour or musty, which would be signs it has possible mold growth in it. If at all possible, maybe try and find a different batch of hay to give her.
If you can't find any different hay that she will eat, she needs adequate amounts of food one way or the other, or her health will suffer. So if she's not currently eating enough to maintain a healthy weight and her fecal poop is getting too small because of the decreased food intake, she either will need a lot more foraged foods, or you may need to find a good quality rabbit food pellet or hay pellet to supplement her feeding until you can get the hay sorted out. Though if doing rabbit pellets, make sure they are a reliable good brand and that they are introduced into the diet gradually. If you aren't sure if she's eating enough or not, I would weigh her regularly as well as feel along her back to make sure she is maintaining a good weight and not experiencing unhealthy weight loss.
Another thing to consider when a rabbit stops eating a particular type of food, like won't eat hay but will eat all of their other food, is that they could have a dental problem like molar spurs, causing sores in their mouth to hurt when they eat that particular food. Increased water intake can also be a sign of a dental problem, because it hurts to eat so they will try and sooth their sore mouth, and fill their stomach up with drinking. So if you have access to a good rabbit vet, it might be a good idea to have a dental check up done.
http://www.mybunny.org/info/dental-problems-in-rabbits/
(link has medical related photos)
https://lbah.com/rabbit/rabbit-teeth-conditions/
