Thank you for saving this bunny!
I think the only way to get a bun to try new food is to try offering small portions of it many times. You can cut back a bit on the alfalfa pellets, but dont stop them completely, or the bun might starve because she doesn’t dare try new food. She should have grass hay available to her 24/7. Alfalfa pellets are recommended for buns up to 6 months of age, so she hasn’t been given inappropriate food – but you do want to wean her onto grass hay and adult bun pellets now.
How is her living arrangements? If a bun has spent most of its life in a cage, suddenly having lots of space might make the bun feel insecure. It can be good to let her have a cage or limited-size enclosure for starters. She should have a hidey-house (an upside down cardboard box with “doorholes” cut out will work excellently). If the rabbit has a home base where she feels secure, she will be more apt to explore the world outside her safe place. It can still take quite a bit of time though, since this bun probably never had good experiences involving humans. You will need a lot of patience.
As for your allergy, it is possible to become allergic even if you werent before. It is also possible to be allergic to some individuals and not others -or you could be allergic to hay or even alfalfa. You can try an OTC antihistamine like loratadine or cetirizine (the type of antihistamine that won’t make you drowsy).