Why must my bitch hump me like a boy?

I have a female boxer puppy at home named Sadie. She has a thing for humping my fiance and me, but has taken a real liking to my leg as of late. I thought only male dogs would hump like that, since it is their sexual position. How does a female learn such things and why do they even want to do that?

First off I should say that some have asked why I allow her to do it. I don't let her continuously do it, but for a moment it is hell-arious. For instance, yesterday she humped my leg and I allowed three thrusts. Why? With each one she farted loudly, and that is the best laugh I had all week.

So I asked Jeeves about this, and he lead me to some answers. The best site, Vetinfo.com, said this:

Spaying a female dog will sometimes result in an increase in testosterone influence, if they produce androgenic (testosterone-like) hormones at higher levels than most females and then the suppressing effect of estrogen is removed due to spaying. This can cause an increase in aggressive or dominance behaviors and that can mean that mounting (humping) behaviors will occur.

That all makes perfect sense, because she was spayed a month or two ago, and happens to be very dominant over other dogs, and she's very non-discriminant about it as long as the other dog isn't toering over her.

The article also said this though:

Whether or not you should be concerned is hard to say. This is actually
relatively normal behavior unless it does get so prevalent that you have to consider an obsessive/compulsive or anxiety based cause. In those cases, there are medications that can help, such as fluoxetine (Prozac Rx) or clomipramine (Clomicalm Rx).

Whoah...give my dog Prozac...share my precious prescription. That's crazy talk. Or is my dog crazy? Or is my leg just really attractive?