Well the last sentence of Phoebe's paragraph there that the article conveniently left out was this: "This book I really connected with as I found there was truth in every word that Levenkron wrote and it helped me comprehend what people close to me have gone through."
So, it's possible some of Phoebe's friends practiced self-mutilation, or she knew of people who did. It is possible maybe she did as well, but self-mutilation most definitely isn't necessarily a sign wanting to die at all, it's usually the opposite. It's a way to transfer emotional pain into physical pain. As the Goo Goo Dolls song goes "you bleed just to know you're alive". Also, I've read a lot more about Phoebe from her friends from joining various groups on facebook and everything I read just talks about how happy and optimistic she was. Granted, it's very easy for some people to put on that happy persona so we'll likely never really know what was going on in her head.
It's definitely a more common thing among young adults, I'd say particularly girls, then one would think so to be honest I don't find it strange or telling at all that she would choose this.