It would have to stem from a new found disdain for men... all men. Maybe the pursuit or the acquisition of the power changed her somehow, someway (ie Raistlin from the Dragonlance series).

Could be an interesting back story.

As soon as someone gets a taste of power and they like it, it would definitely cause perceptions to be skewed.  If you were to reference it to say slavery, where a slave becomes free and suddenly has the power to free other slaves.  That person would then start using their abilities to "help" others.

A different direction could even be that perhaps upon seeing her body transform, it excites her to see other females transform and so she would take any opportunity to make other women bigger and more muscular so that she can watch the show.

The last reason could just be pure insanity and she simply wants to dominate all the males in the world with her own female super army.

An alternative (although I quite like TC2's idea about getting a thrill out of seeing the transformation of other women, too) might be that she suffered some form of trauma that her powers were unable to fully protect her from; possibly she is drugged and assaulted; the drugs keep her from effectively using her powers and the assault leaves her feeling victimized.  Desiring to never be a victim again and wanting to save other women from the same fate, she goes about her plan the transform the female population.  Probably without fully considering the consequences...

I've always thought the 'absolute power corrupts' is a bit of a cheat. Unless she is a completely disgusting cynic (Who are boring), from her perspective, she's doing good - or trying, like most of us.

I'd say it's something that gets started, and she is forced to do more and more to keep it from becoming an even bigger mess than it is, in a butterfly effect sort of way. From that perspective maybe you need to work out what her ability can and can't do - maybe her psuedoscience quantum tweaker can *only* improve women, but when she helps a woman, it affects woman according to how similar their mitochondria is. So she can't help any woman, without improving all of them . . . some. And once you've turned your best friends cousin into the school bully because you helped your best friend, you have to help the japanese girls she's picking on . . . of course, then you have to fix  . . .

I leave the rest as an exercise for the student - <G>. Plus, I suck at writinng - <G>

Pug