What does she feed, pellets I suppose, or forage? Keep that diet up for now.
Anyway, hay is rather unproblematic, just offer a handful for a start. The rabbit most likely will turn it's nose, that's normal with new stuff, just keep offering and replacing it. Making munching motions with your hand in the hay for a minute can help making her to try it.
After a few days, or when she started to nibble it I would give fresh hay at feeding time with the usual routine and refill the pellets (or whatever) an hour later.
It could also be helpful to leverage a rabbit's natural inclination to forage, so not only offering hay in general, but offer a lot across several spaces-- this can trigger curiosity, making a rabbit travel from one spot to another, and then decide to nibble on the best pieces in each spot.