One issue I've noticed reading stories on free feminization fiction sites like Fictionmania is that a lot of readers really don't like dominant women. I hope that as my readers pay money for my eBooks, they are a self selecting group. In other words, if you don't like it you won't buy it.
With that said, it still is a fine line to walk. One of the things I've been proud of in Welcome to College is that Amanda doesn't go out of her way to torment Kylie. She does do a lot of cruel things to him, but she does it because she has a motive rather than just wanting to see him suffer. At times, she can even save him.
There was a real Amanda when I was in college and though I didn't always want to go through with the feminization, I never thought she was overly cruel. The trick is in writing a dominant woman so that she is still dominant and at the same time not a monster. I am running into that issue with a supporting character as I finish Welcome to College. I hope that I have made it work.