Does she know what causes this?
I'll weigh in with what I think is a plausible explanation but YMMV. Recall that in June 2009, the evil liberal David Letterman of See-BS uttered these seething words of pure hate:
"Sarah Palin went to a Yankees game yesterday. There was one awkward moment during the seventh-inning stretch: her daughter [Bristol] was knocked up by Alex Rodriguez."
And then the floodgates were opened wide. Liberals of all stripes characterized poor Bristol using offensive terms like "slut", "floozy", "whore", "strumpet" and other such language that decorum prevents me from repeating here on Free Republic, a family forum.
As I see it, the endless torrent of hate may have effected young Bristol Palin, not yet reaching adulthood at that time. She was vilified like no other has ever been and subjected to an unending stream of malicious mockery. Words do indeed have meaning and they can leave scars. While not excusing this particular case of poor decision-making on her part, I believe that knowing the context that led up to this is important. Recall that the left is the enemy and they seek to destroy all that's good and wholesome. In conclusion, I see that Miss Bristol Palin was specifically targeted for attack by the lamestream media, led by the reprehensible David Letterman and she was wounded deeply.