Mrs. Kemp in dormitory

Good question. I wondered the same thing. My interpretation is that it is supposed to symbolize that she is stuck in "the system" but secretly she wants to be "free", here symbolized by her walking around naked. She does this as a simple act of defiance. This is also somewhat backed up by the scene where she is eating with the crusaders and they are offering her everything off the table and doting on her, as if they can sense she is one of them. At first I thought they just had school boy crushes on her (she is an attractive older woman), but I think it is more than that. They can sense she also doesn't like the system, and so they feel a kinship with her. That's my take anyway.

Well said, I will have to watch it again with your thoughts in mind.

My first instinct was that she was merely acting out a forbidden fantasy -- doing something naughty while the boys were outside playing. "If they only knew what I was doing in here..." -- that sort of thing.

As I recall, however, at the end of that sequence, she looked over her shoulder and gave the audience a pitiable expression of hopelessness: "this is what my life has come down to." The sadness on her face was sobering. It was a good way of showing that there were human beings whose souls were being crushed by the same system that gave us "Run In The Corridor!" and "Out of my way, scum!"

Running around nude might be shocking in itself, but that over-the-shoulder gaze at the audience showed that she was begging the audience not to judge her. That might be the only adventure she can allow herself as the wife of Mr. Kemp, the man who played the recorder in bed before going to sleep.