[6] McDonald was selected for the first time for Scotland Women XVs in January 2020, when she was invited to join the Scotland squad for their Test match against Spain and earned her first cap as a replacement for Jenny Maxwell when she was injured.
[7] Speaking about her role in the match, the team's coach Philip Doyle stated,"Young Mairi McDonald coming in as scrum half.
She showed a very composed performance against Spain off the bench which really impressed us as a coaching group.
[11] She was substitute for Scotland's win against Wales, in which Jenny Maxwell returned to scrum-half.
McDonald first started playing rugby in second year at Hyndland Secondary School under the guidance of her PE and History Teacher.