No you're not a rotten mother. I think we treat all our kids differently and frankly, they are different. It wouldn't make sense to treat them exactly equally.
Both of mine are girls. With my oldest, I had to grow thick skin and be more stubborn than she was. It was noisy in this house for a couple years.
With my youngest, she's just starting the teen stuff, but she's totally different in many respects. I don't have to raise my voice to her, well rarely. She does her homework, etc, etc. She's much easier for me to deal with.
I don't have any experience with boys vs girls, but I do know the trouble I got into. I am pretty strict with them.
Or was, my oldest is now 21.