Gillian attended Reading Memorial High School, was a four-year varsity swimmer and was named a league all-star for four years. In her senior year, she was captain and led the team to its first state title. Gillian won the sportsmanship award in 2008 and 2010 and the `heart and soul' award for dedication and determination in 2009. She holds school records in the 200 and 400 freestyle relays.
Gillian is from Reading, MA and is the daughter of Denis and Deirdre Walsh. She has one brother, Christopher (21) who attends Boston College and is a senior on the Men's Swimming and Diving team. Gillian swims for the Burbank YMCA Bluefins.