In high school, she was her school’s 2006 Rookie of the year and its most valuable player in 2008 and 2009. During the 2009 PWHL playoffs, she was the leading scorer. Mercer competed for the Bluewater Jr. Hawks in 2009-10 and was also captain of the team. In addition, she was one of the top five scorers in the PWHL during 2009-10.