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.