[2] Harmer made her county debut in 2015, for Norfolk against Cumbria, in which she took 4/18, which remains her List A best bowling figures.
[4] The following season she achieved her List A high score, hitting 60 against the Netherlands, and was her side's leading run-scorer in the County Championship.
[8] Ahead of the 2019 season, Harmer joined Essex, helping them to third place in Division 2 of the County Championship.
[14] Harmer was named in the Lightning squad for the 2020 Rachael Heyhoe Flint Trophy, but did not play a match.
[17][18] She played seven matches for Lightning in 2022, across the Charlotte Edwards Cup and the Rachael Heyhoe Flint Trophy, scoring 105 runs.