I´m late... but about Andy ruining Edie...
Edie´s mother gave Edie pills when she was young, to calm her down. Both Andy´s and Brigid´s mothers gave them pills when they were young, so it´s not that weird that they turned out the way they did.
And the fact that people never tried to stop Edie... I mean, everyone was doing loads of drugs then, I don´t think she was that much worse than anyone else.
I have read Mary Woronovs book, Swimming Underground, and, besides being very good and very interesting, it´s also really scary how much drugs they all did.
And when you´re into drugs, you love it more than you love the people around you.