Joss Whedon is known for writing "strong female characters" in many of his stories. Or, more accurately, most everyone else on TV is known for not writing strong female characters in their stories.
Essentially, Whedon females will always fit into one or more of the following four categories:
Hot Kickass Women
The vast majority of women with combat skills in Joss Whedon shows have them because they were either neurologically or magically conditioned to have them. There are some notable exceptions (Zooey and Saffron from Firefly to name two) but for the most part these women did nothing to attain their phenomenal combat skills. They were forcefully given these skills by the government or destiny or whatever, and now they're constantly being put into positions where they have to fight.
There are three clear-cut examples of people who fit exclusively into this category: Drusilla after being tortured, River Tam, before tapping into the combat training the government put in her head, and Winifred Burkle, in and around the time she spent trapped in a hell dimension, in the third season of Angel. But honestly, give any Whedon female character enough seasons on the air, and sooner or later, she'll fit into this category. Buffy in season 6, Faith in season 1 of Angel, Echo in every third episode of Dollhouse; they'll all face some traumatic event and cope with it by turning into a loose cannon who is simultaneously extremely vulnerable and constantly spewing word jumbles.
Hot Women with Dignity
Archetypal examples of this include Adelle DeWitt from Dollhouse, Inara from Firefly, and Lihla from Angel. These women are refined and posh. They all have excellent posture and sexual indiscretions.
Geeky/Awkward Women...who are also Hot
And of course, every show has a beautiful geek who for some reason has trouble getting the equally geeky guy. Fred Burkle, physics genius really never got a chance with Wesley Wyndom-Price. Kaylee Frye, mechanical phenomenon didn't seal the deal with Simon until the end of the movie. And Willow had about three seconds with Zander before she gave up and switched to women.