Which superior officer did Princess Elizabeth II report to during her service as a junior officer in WW2?

During the period of her training, Elizabeth was under Junior Commander Violet Evelyn Wellesley (196395), who was commander of No. 1 Company, No. 1 Mechanical Transport Training Centre (Camberley), part of the Royal Army Service Corps Training Establishment at nearby Aldershot.

Violet or "Vi" Wellesley was born on 15 August 1897, and died on 29 August 1971, per Burke's Peerage as cited online at thepeerage.com. Her paternal great-grandfather Rev. Gerald Valerian Wellesley was the younger brother of Arthur Wellesley, the first Duke of Wellington; thus, she was someone of suitable aristocratic background to be trusted to take charge of the princess. She was awarded the MBE in 1946 and eventually left the Army with the rank of Major (WRAC ranks were normalized in 1952).

She appears in the Army List for the first quarter of 1945, under the Auxiliary Territorial Service, as

Wellesley, Miss V. E. (W.S./Sub. 9/11/41) (T/J. Comd. 11/9/42) 30/5/41 (7/12/40)

where the odd rank and date listing is a reflection of the status of the ATS as a formerly-volunteer organization later joined to the Territorial Army. The same list shows Princess Elizabeth in a special capacity, after the senior leadership but before other officers:

Hon. 2nd Subaltern H.R.H. The Princess Elizabeth, Col. Gren. G'ds. 24/2/45

Overall leadership of the RASC Training Establishment is listed too, but not down to the level of individual training battalions or companies. The commandant was Brigadier Frederick Clover, who eventually retired as a Major-General, and was named Aide-de-Camp to George VI in 1946, possibly in partial relation to his supervision of Elizabeth's tenure in the training establishment.

While these lists do not show the command structure, contemporaneous reports allow us to reconstruct the circumstances of Princess Elizabeth's service. Sarah Bradford's 1996 work Elizabeth: A Biography describes that:

For some time past, Junior Commandant Violet Wellesley (known as "Auntie Vi" to her subordinates, as Elizabeth was to discover) had been coming over to Windsor to teach Elizabeth to drive in preparation for the course, which was intended to make her not only an expert driver but also capable of maintaining the various vehicles she would have to drive.

Recollections by Eileen Kennett Heron (later Hall) give some more detail. (Note that as an NCO she is not in the Army List excerpted above.)

At the beginning of February 1943 I found myself at No1 Company "Beaufront" – a company exclusively doing instructor’s courses. The J.C. (Junior Commander) was Violet Wellesley, a great niece of the Duke of Wellington, tall and thin, very like his portraits and a somewhat formidable character.

Heron was later attached to No. 3 Company, based in "an enormous and beautiful house on the Portsmouth Road" known as "Mulroy".

In January 1945 D.I.s came back saying that they had seen J/C Wellesley out on driving instruction with Princess Elizabeth. In early March I and two other girls from Mulroy were told to go and see our Commandant at 6.00 pm. I presumed it was for an overseas posting! On arrival we found eleven other girls three from other companies. The Commandant informed us that we were going on an N.C.O.'s course that included H.R.H. Princess Elizabeth who would be an honorary Subaltern. We were not to tell anyone, preferably including our own families until after the event.

At the end of the course H.R.H. Princess Elizabeth and J/C Wellesley drove up to Buckingham Palace in uniform and in an army vehicle for a garden party. They were stopped at the gate and asked for their identification cards.

The document includes a contemporary photograph describing Wellesley as "H.R.H.'s driving instructor", taken when the King and Queen were visiting. Other photographs, from an album kept by fellow student Peggy Hinchcliffe, also show Wellesley during the visit, appearing as the instructor (and nobody else seems to be named in that capacity). Some other descriptions of the Queen's service describe her as having been in No. 1 "Beaufront" Company, which was the unit commanded by Wellesley (it was named for its location in Beaufront House, which like Mulroy was on the Portsmouth Road, Camberley).

A similar photograph from Wellesley's own collection is annotated in similar terms: "Violet Wellesley pictured in her role as chief instructor". That collection also includes a letter from Elizabeth of 1947 thanking Wellesley for a wedding gift, and saying -

I tried to teach my sister how to drive, when in Scotland this year. It was nerve-wracking, and I now know what you must have felt like instructing me!

On the basis of Eileen Heron's account, and confirmed by the several independent sets of photographis, it looks like Wellesley was in charge of that select group of students, in addition to having provided informal training to Elizabeth beforehand. Other personnel giving instruction seem to have been sergeants, with Wellesley being the officer in charge. I would guess that her involvement began because Elizabeth was keen to take part in some military service, and Wellesley was part of a distinguished family who worked conveniently close to Windsor, and therefore might have been drawn to the notice of courtiers. The organization of the specific course seems to have been shaped around the princess, and the visit to a garden party feels like a continuation of that relationship - one whereby Elizabeth could be temporarily slotted in to the military system, by virtue of a suitable society connection.

Elizabeth's promotion later in 1945 was after V.E. Day, and it does not appear that she was part of any military unit at that time. By the Army List for the fourth quarter of that year she was shown as "Hon. J. Comd. H.R.H. The Princess Elizabeth", so again in that special honorary capacity rather than in the main list of officers. Other serving aristocrats and members of the Royal Family appear to be listed more substantively. So I think she no longer had a regular officer commanding.