It seems to me your girl was manipulated by the societal climate to report you. It has more to do with pressure and how society currently stands. It seems it didn't have much to do with how she viewed the activity, at least at first.
In an ideal society, she would have the right to tell you, at any time, she wants such activities to cease. At that point, if you didn't stop, yes, you would deserve some form of legal punishment.
I don't know your full story, so I'm just telling it as it seems to me. I don't know the situation of how/why she reported you. Couldn't she have just blabbed to someone, even another child, about the activity, perhaps just looking to show off?
I got the feeling the activity you did with your girl lasted quite a few years. It seems she just changed her mind, but never shared her mind-change with you.