Historically Japanese nuns / priestesses did not actually shave their heads. They actually just trimmed it to the shoulders (in general ladies had very long hair). In Tale of Genji and other literature from the Heian period it is described like this.
It might be that they cover their hair rather than shaving it off.
Thanks Huseng. I recall seeing one Buddhist marriage ceremony in Japan on Youtube and the presiding Zen priestess was bald and I thought perhaps this head covering was meant as protection against the element of cold in winter or protection headgear like how some of the Bhikshunis sometimes wear a winter cap or head covering... For a moment, the longer pic below reminded me of the Catholic Sisters lol