Good question and observation. All the comp0ound women seem to have the obligatory compound hairdo. I suppose its just traditional and perhaps utilitarian, in that it makes maintenance of long hair easier.
Its a very unflattering look, especially on Nicki. She looked so much better with her hair cut short.
It is unflattering, and I think that's the idea--a woman's hair would only be let down for her own husband (and in front of her sisterwives, of course).
I noticed Lois had cropped her hair, and there was one scene where Frank tried to throw away her braid and she snatched it back. It meant something to her even then.
I LOVED the gal in one of the very last episodes whom Nikki drove to the compound and picked her up, hiding behind a tree. She had HUGE hair. *HUGE* -- it was like six inches up off her head! She was this scared little mouse. But adorable.
This was borrowed from the actual practice among Fundamentalist Mormon women of wearing their hair as high as possible on the grounds that this added height brings them closer to God.