Surely you aren't implying the Princess Elizabeth was conscripted for military duty?
No, but From spring 1941, every woman in Britain aged 18-60 had to be registered, and their family occupations were recorded. ... In December 1941, the National Service Act (no 2) made the conscription of women legal. What the photos demonstrate is that no matter what your station in life is, when your country is at threat of invasion, everyone is expected to do whatever it takes and if that means getting your, or should that be, one's, hands dirty, so be it.
During WW2, the women of Britain worked in the factories, drove the buses and trains, did every sort of job no matter what. Many did serve in the armed forces, they were not drafted into combat units, but could volunteer for combat duty in anti-aircraft units.
'Ack Ack Girls' were members of the
Auxiliary Territorial Service (ATS) that helped operate
Anti-Aircraft Guns in the defense of Britain from German bombing raids during World War 2. Princess Elizabeth was in the ATS.
Ack Ack was not the noise the weapon made but a euphemism for Anti-Aircraft Gun.
By the way, the photos of the then Princess Elizabeth are not from the British press, they were taken by a press photographer for The Washington Post.