As a woman reading this article and the response, it seems to me that your idea of nice is fundamentally different from hers.
The author describes her experience as being the nice girl as actively harmful. To maintain this persona of sweetness, she let people walk all over her and sacrificed her own needs to address those needs around her. As women, we are socialized to do exactly this… i.e. do everything to make yourself smaller, and make people comfortable around you. This leads to a lot of self-doubt, hesitation and denial of the vocalization of our true opinions.
While being a genuine and good person are both things to strive for, I know the pain the author struggles with. Like many women, I’m empathetic and want to help those around me if I feel they’re in pain, and prevent my presence from adding to it. Niceness is a symptom of the larger condition of women’s oppression, which is where your understanding differs from her point.