Simon made her Broadway debut as the composer of The Secret Garden, for which she was nominated for a 1991 Tony Award for Best Original Score and a 1991 Drama Desk Award for Outstanding Music.
She recorded and performed as a singer and songwriter, and was known for the musicals The Secret Garden (1991) and Doctor Zhivago (2011).
Simon won a Grammy Award in 1981 with her husband, David Levine, in the Best Recording for Children category for In Harmony, and again in 1983 in the same category for In Harmony 2.
Simon received Tony Award and Drama Desk Award nominations for composing the music for the Broadway musical The Secret Garden.