HH I would guess that she was only considered for a GM as she was a nursery teacher whereas a grammar school teacher might have merited a GC had they been head of department etc.
The tariff system strikes. In my father's line of business the basic award was OBE but no CBE. - PN
Not strictly so, since the only "tariff system" applied in such cases is that of bravery, as indicated by the attached extract from
https://www.gov.uk/honours/types-of-honours-and-awards
"
The George Cross
First level civilian medal for bravery: for acts of heroism and courage in extreme danger.
The George Medal
Second level civilian medal for bravery: for acts of great bravery.
The Queen’s Gallantry Medal
Third level civilian medal for bravery: for inspiring acts of bravery."
IIRC from my time in the Naval Secretary's Office, the QGM was introduced in 1974 with the very specific aim of replacing an Order of the British Empire award for bravery based on rank.
Jack