Honoria studied medicine at the University of Glasgow and graduated MBChB in 1910; she was registered as a medical practitioner in April of the same year.

[1][2] She worked initially at Glasgow Royal Asylum, Gartnavel, and as House Surgeon at Kilmarnock, then joined the Girton and Newnham Unit of the Scottish Women's Hospitals in 1915.

[1] She served as a medical officer first in France (Domaine de Chanteloup, at Sainte-Savine, near Troyes) with Scottish Women's Hospitals, and then in Salonika.

[1] For her wartime service she was awarded the French Croix de Guerre and Médaille des Epidémies, and the Serbian Order of St Sava.

Keer was described by one of her colleagues, Isabel Emslie, as ‘a strange mass of contradictions: serious, reserved, and with very correct old-world manners'; at the same time, 'her sly wit was a constant joy’.