She studied piano with Julian Rossetti, and with Carlo Albanesi at the Royal Academy of Music (RAM).

[3][5] In 1918 she joined Mary Ramsay and Oscar Beringer for a benefit concert of works to two pianos, at London's Aeolian Hall.

[13][14] Critics generally praised Mackinnon's technique and choice of programme,[6] though Scriabin was considered quite "futuristic" in the 1920s.

"[17] The Guardian expressed admiration for her charm and intelligent choices in 1932, but some disappointment at her restraint, when "something more of audacity is wanted.

[20] She wrote Music by Heart (1938), "the only non-technical book in English devoted primarily to memorization", and "a classic", according to a 1955 review.

[21] During World War II, Mackinnon taught at Dominican College in California, and at Bradley Polytechnic Institute in Illinois.