Sure, Alison was Alison. She was the shoulder to cry on, the only one you'd ever want calling up your crush to find out how he felt about you, and the final word on whether your new jeans made your butt look big. But the girls were also afraid of her. Ali knew more about them than anyone else did, including the bad stuff they wanted to bury - just like a dead body. It was horrible to think Ali might be dead, but...if she was, at least their secrets were safe.
And they were. For three years, anyway.