You have a skewed notion of the concept of chivalry: it has always been about defending the gentle lady and not the expendable peasant. Andres Capellanus, in The Art of Courtly Love, recommended that a nobleman who was attracted to a peasant girl praise her until she'd let down her guard, then rape her. Even among the nobility, chivalry could be much more of a theory than a law - the counts of Blois and Nantes both attempted to abduct and rape Eleanor of Aquitaine so that she would be forced to marry them and they would gain her lands - but in general, the rape of a highborn virgin was more important than the rape of a highborn non-virgin, and the rape of a highborn non-virgin was much more important than the rape of any poor one. By the Victorian era, this was sadly barely changed. As I wrote in this answer, a woman had to explain, if not prove, that she had struggled to the point of exhaustion against a rapist and then fainted before being penetrated or else it would be strongly suspected that she had given in, and therefore consented. Adults and teenagers would frequently have doubt cast on their virginity prior to rapes, and if a nineteenth-century unmarried woman had had premarital sex, it would be assumed that she might be willing to have sex with anyone, including the rapist. All of this was particularly an issue when middle-class doctors were investigating the claims of working-class women, whose lifestyles did not always match up to the sexual standards of the middle and upper classes.

Regardless for the potential to be hogwash, the point being that duels were always a possible backlash to libel. So why not assault when physical presence was involved? Did assault for categories of such behavior not exist?

Dueling is not at all my area, but I can tell you that the duel was part of the aristocratic way of life, and in short it therefore had no relevance to late nineteenth-century women working in offices (and had no relevance to anyone in the twentieth). I would recommend /u/georgy_k_zhukov's answers on dueling for more information on the relationship between dueling, honor, masculinity, and class, but basically: dueling was never a possible backlash to workplace assault or harassment.

I understand the repercussions of economic reliance might be a factor, but I don't recall a theme of cases by rich women against their bosses, I simply recall the advice to quit.

Again, I think you have a misconception underpinning your question: rich women did not have bosses. In the early twentieth century, women largely worked because they had to support themselves. Maybe an unmarried woman moved to the city in 1925 and became a secretary to pay her rent. Maybe her husband was overseas during WWI or WWII and she needed to put food on the table for her children. If she came from money, she would stay at home and live a life of leisure until she married. If she were married to someone who could provide for her and their children, she would manage the house. There were rare circumstances where married women with no need to do so had jobs in offices, but by and large, there weren't women who both a) had bosses that might see them as fair game and b) had the financial wherewithal to support themselves if making an accusation caused them to lose their jobs.