A native of Whycocomagh, Cape Breton Island (Nova Scotia), Gillis graduated from Bowdoin College in 2007 with a major in government and legal studies and a minor in English. A highly decorated women's ice hockey player at Bowdoin, Gillis was named the NESCAC Rookie of the Year in 2004, as her 24 goals and 19 assists left her with the highest point total both on her team and among conference rookies.