MacKinnon attended the University of British Columbia where she played ice hockey for the UBC Thunderbirds.[1] During the 2021–22 season, as a junior, she tied for the league lead in goals with 10 and finished second in total points with 21. Following the season she was named the Canada West Defencemen of the Year.[2] During the 2023–24, in her final season, she served as team captain and recorded ten goals and 12 assists in 26 games. She led all defensemen in scoring with 22 points. Following the season she was named to the U-Sports First Team All-Star team. She helped lead the Thunderbirds to three consecutive Canada West Championships and a bronze medal at the 2023 U Sports Women's Ice Hockey Championship.[3] She finished her career as the team's all-time leader in points by a defenceman with 34 goals and 47 assists in 126 games.[4][5]
After going undrafted in the PWHL Draft, MacKinnon was invited to the Toronto Sceptres' training camp.[6][7] In Toronto's final pre-season game against the New York Sirens, she had a team-high 23:04 of ice time and recorded an assist.[8] On November 29, 2024, she signed a one-year contract with Toronto.[9]