Missy has led the show jumping and equitation training ranks for years. She and her husband John Brennan own North Run, which is located in Warren, VT and Wellington, FL.

Missy grew up in East Aurora, NY where she learned to ride under the watchful eye of her mother, Doris Clark, a locally renowned horsewoman. Together, they began their business, Fox Run LTD. Missy later went off on her own and started North Run. As a junior rider, Missy was a working student for Chuck Graham, a well-known Buffalo, NY professional. She then rode jumpers with George Morris and Rodney Jenkins, and spent some time working for Jimmy Lee.