Born in Darby, Pennsylvania, Horan graduated from Long Island's Hofstra University with a degree in theater performance. Rosenthal also attended Hofstra shortly before Horan did, and she frequently heard of his reputation for punching up productions with his impeccable wit. One night, Rosenthal returned to his alma mater to see a play, which she happened to be appearing in, and thinking she was funny, he pursued her and romance followed. The couple married in 1990 following Horan's conversion to Judiasm.
Her theatrical credits include the Off Broadway production of Rosenthal's breakthtough production "Tony 'n' Tina's Wedding" and "Vampire Lesbians of Sodom" in Los Angeles. She was a founding member of Actors Initiative and has also appeared as a sketch-comedy performer with the group Artificial Intelligence. The actress' television credits include a recurring role in "General Hospital" and guest appearances in "L.A. Law," "In Living Color," "Down the Shore," "In the House" and "Coach," but audiences grew fondest of in the role of "Raymond's" Amy, which she began playing in 1998 in what was initially planned as a one-off guest spot. Both the series creators and fans of the show responded to the loopy chemistry between Horan and Garrett and she became a recurring character--when the relationship was briefly sidelines, viewers calmored for her return, and Horan was formally added to the cast when Amy and Robert finally tied the knot in 2003.