Passing a polygraph is not some impressive thing. They are unreliable, false positives and vice-versa happen all the time without the user doing anything, this is why they aren't allowed in court and why most countries don't use them in investigations at all anymore, American LE typically only use them today to see if the person is willing to take them which is a horrible practice since no one should, any half-decent lawyer will tell you to reject them whether you are guilty or not as they've played a major role in wrongful convictions. She was fortunate that this happened during a time polygraphs were still seen as accurate, that's all.
She didn't deceive LE she pretty much came out and admitted it was her in her second interview after they clearly described her once they became suspicious and then she went home and confessed to her mother, her arrest was clearly imminent at that point. This story is not about a teenager who deceived police and was close to getting away with it, it's one of countless stories advising against the use of polygraphs as her passing it is the reason it took them six months to look at her closer.
I can't imagine what you said because she was not at any time savvy, luck and timing bought her six extra months.
