It's actually not pejorative. (The term "wenching", however, is. Go English language! :)
I've linked elsewhere: First defn from first hit on google: http://www.urbandictionary.com/define.php?term=wench
I've linked elsewhere: First defn from first hit on google: http://www.urbandictionary.com/define.php?term=wench
wench (wnch)
n.
1. A young woman or girl, especially a peasant girl.
2. A woman servant.
3. A wanton woman.
intr.v. wenched, wench·ing, wench·es
To consort or engage in sex with wanton women. Used of a man.
and http://www.merriam-webster.com/dictionary/wench: a lewd woman : prostitute