The only reason? Doubtful. Sometimes people want to get away from the group for some peace and quiet. Sometimes they want to see what drugs are in the bathroom cabinet. Sometimes they just explore somebody else's house. Who hasn't done that as a teenager? Get your mind out of the gutter, American Thinker.
This is what I believe is most likely to have occurred.
What I believe is that it never happened. Something happened to her somewhere sometime with somebody. But the details she gives now probably don't correspond to an actual incident at that (unspecified) time and place. It's a vivid but false memory that she has come to believe over time.
I distinctly remember that Crappie weighed 8 pounds, if only I had went to an official weigh station.