My parents were sort of hippyish but I think even they'd balk at calling their first born child 'Mistress'. I acquired the nick on misc.fitness.weights for my, erm, uncompromising discursive style and attitude about working out. So I guess #3 would be the closest: 'something personified as female that rules, directs, or dominates', although 'achieving mastery in the field' strikes me as appropriate too (although the more I know about training the more I realize how little I know). The S/M flavour to it also pleases me.
Since I took on the nick, I've gotten a lot of email from men who want to pay me money to beat them up. It doesn't seem like such a bad line of work.

I've also gotten email from real dominatrixes (dominatrices?) who are curious about my employment. They seem to like the idea that I get paid to order people around and inflict pain, just in a different way. Someone from misc.fitness.weights even wrote a song, 'Working for the Mistress' which described the imagined benefits of being my houseboy and getting one's ass kicked by me in the gym. The mfw folks are endearingly creative.