Dempsey has represented the United States women's national ice hockey team at the 2011 4 Nations Cup. She played for the Harvard Crimson women's ice hockey team from 2009 to 2013. She is a graduate of the Rivers School and Harvard College, where she majored in Classics. During her time at Harvard, she lived in Pforzheimer House.
In August 2013, she was selected as the 10th overall pick by the Boston Blades in the 2013 CWHL Draft. She would be awarded the CWHL's Rookie of the Year Award in 2014 after leading all American-born players in league s coring. The following season, she was a member of the Blades roster that won the 2015 Clarkson Cup.
In 2016 Dempsey became a fifth grade Teacher for fifth in her home town of Winthrop.