That story about being a mechanic during the war and actually doing that job is a myth, in the last few weeks of the war she did enlist and do the photo ops and image thing, but it was never real and she went home to Windsor Castle every night.
“She was enlisted as 230873 Second Subaltern Elizabeth Alexandra Mary Windsor in the Auxiliary Territorial Service, the ATS, [March, 1945] and sent to train as a transport officer at Camberley. The course was three weeks and Princess Elizabeth did not associate too closely with her fellow trainees.
She lunched in the officers’ mess and slept the night at Windsor Castle”
I have no doubt what you posted is accurate and that her wartime service was a myth...but perhaps it was just the myth the English people needed at that time. When it comes to creating myths and legends to provide much needed morale and rally people to a cause, the English are hardly unique, just possibly more skilled than most.