I didn't read the article that you are referring to so I am not fully familiar with the topic, but you raise a good point. People should have the right to make decisions about their own body. That is their freedom. I would hope that it is her choice for real though and that she is not being exploited behind the scenes. With the prevalence of human trafficking you never know these days.
But again, if she is free then why not I suppose?
I linked to some other articles similar in the post. It doesn't seem like she is the ONLY one that has done this.
She could get drunk (under age drinking... see banning doesn't work) at prom or some party and lose her virginity, and have nothing but a hangover and maybe an STD as her reward.
If she makes $2.9 million from it in a more controlled fashion people are outraged. Seems kind of stupid to me.