It was probably mutual on both their parts, but the law holds that the minor has no choice in the matter and defines this act as sexual abuse (there may be a more specific term, I am speaking generally).
So, yeah, you know, and I know, and her defense attorney knows, and even the prosecutor and the dang judge appear to know that the sentencing in this case is harsh and probably very unfair. Unfortunately, they are working under guidelines established by their legislature. They cannot make laws to suit what they individually feel is appropriate to each crime, and thank God for that.
Hopefully she gets a re-trial or something via the appeals process, but no one here has actually done anything they should not have. There is no injustice, per se, as, to use the old cliche, ignorance of the law is no defense.
Again, though, I agree that the sentencing is ridiculous when there are real predators out there. Then again, maybe she would have become one. Doubtful in my mind, but who knows.