> Do you think I should pretend to get rid of the vid to make her like me more, or continue to blackmail her to do whatever I want?

No, you should just get rid of the video.
Primarily because extortion is illegal and most likely so is that video.
Simply put, if she's underage, she can report you to the feds and have your ass hauled off the jail for at least three charges that will end your life before it has begun.