Well, if you have canines, then both the word dog and bitch are usual and positive, especially if you're trying to breed!
But, while I understand what you are saying Craven, Deb... possibly even Setanta
... I have heard a woman called bitch or witch for doing precisely what she wants, no more - no less. There is such unequality of the sexes --- throughout the known universe --- that in the few spots where women do stand up for themselves they need all the support they can get.
Just think, if a woman were called bitch in Nigeria, Iran, Saudi Arabia, etc. etc. they'd dig a hole, place her in with only her head showing and toss large rocks.
Craven. That avatar is.... bitchy. Can't you use that sweet Sgt. from Toy Story????