When reducing pellets, it's important to keep an eye to make sure she starts eating hay well right away. If not she could lose weight, so it's always good to monitor a rabbits weight when making any dietary changes.
Also if she doesn't start eating hay better with reduced pellets, it could be your rabbit is picky, so try different varieties. Or it could mean there's a possible dental problem causing the lack of hay eating. When reducing pellets, it's important to make sure the cut and quality of your hay is good, with plenty of leafy strands(as opposed to a lot of mature stems). A cut of hay that is too coarse, is devoid of a lot of nutrients and contains mostly indigestible fiber, which can result in unwanted weight loss and other health concerns.