virago: an ill-tempered, overbearing woman; also, a woman of great strength and courage.
This seems to be a gender specific occurence. Male terms like "dick" are always negative. But I have often heard the term "bitch" used in a positive way. (Though, the term "cunt", suprisingly, is still considered a universally negative term, even after all the years The Vagina Monologs have been trying to rehabilitate the word.)
Anyway, I saw the word of the day and was reminded of many conversations in the past concerning gender.