In 1946, the uniform changed back to a blue blouse and navy skirt, with a beret; the beret was replaced with an ‘air-hostess’ hat in 1964. At the same time the style of the blouse and tie changed, and skirt lengths fluctuated in accordance with fashion. (In 1981, a neckerchief replaced the tie).
I've omitted the re-designs by Jeff Banks and Ally Capellino in 1990 and 2000 respectively, as they're so much later han the books. If anybody knows any of this to be incorrect, please say up! Guides seem to have been one of the uniformed youth movements that had the fewest clothing changes, in fact.
The Brisley frontispiece for In Camp shows them in the recently-introduced dresses, referred to in the text as overalls (the dresses/ overalls would be more laundering than skirts and blouses, but that's perhaps less of a consideration in the CS environment, as well as being cooler in a Tirolean summer)
A rather belated comment on this post.
I was a guide between 1960-66 (when A levels got in the way of Queens Guide and the Rangers). Our skirts didn't vary much in length "according to fashion". Ties were still the folded triangle tied in a reef knot at the back of the neck. Ours were blue but there were Companies which had yellow ties. According to the GG website the "air hostess" hat was introduced in 1964 but in my experience wasn't widely adopted (I "modelled" the current uniform in 1966 at an official event and was given the beret to wear, as did the girl with me).
The Capellini/Banks designs were awful. Could you imaging getting up to Guiding activities in that ankle length skirt? Even in the early 1900s the skirts weren't that long!
We used to parade and line up in patrols at the beginning of meetings and were inspected and the best turned out patrol got points. Difficult to do that in the "practical" modern uniforms. It was a matter of pride for the whole of the Company to compete for this and there was much ironing of uniforms on Friday after school! It was also a matter of pride for us to be in the parade on Remembrance Day without coats (woollies under the blouse - gloves allowed.) We practised marching in step before the event and sometimes we were better than the British Legion members
I don't remember any local Companies changing to the loose 3/4 length sleeved shirt in my time.
As for the 1930s uniform dress. I have photos of my Mother as a guide wearing it. In addition to ease of laundering and coolness in summer, it was cheaper than the woollen skirt, blouse, etc., so more viable for less well-off girls. The cotton dress was still available in my day for camp, etc but I never saw one in use.