Macnab was born in the Philippines in the province of Iloilo where her Scottish parents were based while her father worked for the Hong Kong and Shanghai Bank.
[1] When the family returned to Scotland, Macnab was educated at Kilmacolm before studying at the Glasgow School of Art from 1922 to 1925.
[2] She became a founding member of the Glasgow-based Society of Artist Printers and as soon as she graduated, the Glasgow School employed Macnab to establish and run a class on lithography and colour block printing.
[3][4] Macnab only taught the class for a year, during 1926 and 1927, but her students included Alison Mackenzie.
[6] In 1927 Macnab married James Munro, a chemist, and after she started to raise a family appears to have put her artistic career on hold.