Myself, and most women I know, totally ignore clothing "rules".

There was a time when anything less than ankle length went straight from "proper" to "whore". It's all relative to a particular culture and time. So a modern evangelical woman wearing what is marked "proper" in this photo would have been locked up for indecent exposure prior to WW 1 -- and in some places and subcultures well beyond that. It amuses me that the modern arbiters of propriety and claim to nurture an immutable morality, would have been scandalously improper just four generations ago.

Ironically a major driver of shorter skirts was a shortage of material in WW 2. It had nothing to do with people wanting to be libertines. But the trend stuck.