(No offense, Salon.com guy.)
In this letter and response, the answer is so philosophical and abstract as to be no answer at all. And look how it ends! "Adulthood is not all that much fun"? If that's how he feels, I definitely don't want his advice about my life, I'll tell you that much. (Only ask people for advice who are reacting to life in a way you wouldn't mind doing yourself.)
The real (short) answer? I saw this quote somewhere just the other day: "To find a soulmate, you have to have a soul." Which is just another translation of the cliche "to find a good partner, you have to first become a good partner." Which includes being a whole person.
We're all attracted to partners who are being what we want to be, doing what we want to do. If she's attracted to pierced coffee-shop employees with skateboards, then she's obviously feeling too buttoned-down herself. She closed off her choices too early! Her identity status is obviously in foreclosure, probably in several areas!
And if she doesn't bust out and express that wacky side of herself soon, then she will (I guarantee you) have what is popularly known as a "midlife crisis" in not too many years. Probably after she's married some guy she thinks she's "supposed to" and also had the kids she's "supposed to", who will then be damaged by the whole thing.
The alternative is to do what you love, and then adulthood is pretty dang fun. (I'm not saying it isn't scary.) It doesn't only apply to work. In fact, much to my surprise, adulthood has only gotten steadily more fun with each year. (Now, I'm not saying grad school has always been easy and fun, but that's only a part of it.)
I would recommend she get an identity status interview and see what areas of her self she's foreclosed on. And as she enjoys "snobby" (ok, "hip") pursuits, I would recommend she do some reading on the Shadow Self and take it from there. Go do something "bad"! (But not illegal, as she's not under 18 any more.)