I think they are all equally culpable. Everything seemed to mesh together to make this mess. If KV hadn't put pen to paper, this wouldn't have been an issue. She's as much to blame as anyone else. When I was that age I knew that plagiarism was theft, and that theft was wrong. I knew that when I was 12, when I first wanted to become a writer. I wouldn't have dreamed of trying to lift someone else's work and pass it off as my own, even when my own writing wasn't that original. I don't think age should be taken into account here.
What concerns me is that we are focusing so much on "poor KV, and hope she can get her life back on track"- what kind of message are we sending? Yes, I hope she can come through this and learn some valuable lessons, but she also made the choice to plagiarize. If we are in a stressful situation and decide that doing something immoral will help get us through it, then where do we draw the line? Just because things are stressful, murdering others doesn't become ok, or embezzlement doesn't become ok, or cheating on our taxes, our spouses, etc, or robbing banks- these things aren't ok. Stealing the hard work of another writer is WRONG.
When we find ourselves in positions of potential success, immoral actions do not suddenly become ok or even understandable because things are stressful. We can't shift blame to those around us for our actions, we have to each live out our morality with all the integrity we have. This wasn't about her trying to figure out morality at a young age, as some have suggested, she simply bent with the wind and took the easiest course, which was to steal, proving how little integrity she has. She wasn't even starving or homeless, which might make her actions more understandable- she was in an enviable position.
All of those who supported her in this venture, those who knew what she was doing, are equally to blame, though, L,B, and Alloy, etc. But she still made the choice to steal. She could have said no. If it was all about the money offered, then it wasn't about the writing anyway, and plagiarism proves it isn't about the writing, but stealing a quick buck.
By trying to lessen her guilt by blaming others, we are doing her a great disservice. It is important to face the consequences of our actions, so that we can grow as people. Had she done the right thing, and written an original work, we'd have been happy for her- the consequences would be good. She chose not to do that. Merely having her reputation ruined is only the beginning. The memory of that fades, people forget, and ooh, that wasn't too bad, I could be more sneaky next time and do the same thing again- maybe not plagiarism, but something else in life. She has to be held accountable for this, and so does anyone else who was involved, in equal measure, or we are sending a REALLY nasty message to the next generation of writers. Anything goes. Ethics are out the window.