(Long boring post alert! I actually think my interest in this topic has less to do with Alexa herself, more to do with the sociology of celebrity culture. Like others here, I just enjoy seeing what she wears... no big deal.)
I think I agree more with DiamondSea here, but the comparison with Vanessa Minillo (or any other MTV VJ for that matter) is misleading. Her PR team a failure? Um, look: the girl was invited to sit front row at Louis Vuitton. (There is no conceivable universe in which someone like Minillo would be sitting front row at LV. Or, for that matter, Peaches Geldof.) Consider who else was in that front row, the company Alexa was in. Whoever the Powers That Be at LV are who made that decision (MJ or not)-- that says a lot about the "it"--the allure, the (superficial) cultural currency-- that she presently has. (Whatever the "it" of the "it girl" is, deserved of not... and actually, almost by definition, "it" is not something earned or deserved, but something you simply-- if only momentarily-- have.) It's all the more amazing when you consider that yes, objectively speaking, she's a relative nobody-- i.e. with, objectively speaking, no significant accomplishments to her name. And yet, she's on the cover of high fashion magazines, almost disgustingly gushed over by writers, analyzing her as if she were a kind of "phenomenon," etc.
She is moving to a much bigger pond-- so will be a much smaller fish. But on the other hand, she either already has or will easily gain entree into various different but overlapping NYC circles or "scenes"-- e.g. (high) fashion (with assorted models, photographers, magazine editors, etc.), music (and not just as girlfriend, or appearing in videos: from the job, she's acquired some independent cred on her own-- e.g. as interviewer & DJ), photography/ art (at least the hipstery kind), celebrities/actors, & of course all sorts of socialities, etc. *Of course* she will be photographed, given those circles/scenes-- and significantly, because I think people will want to be photographed with her.
In that respect, I think there is something to the comparison with Edie Sedgwick-- not anything to do with them as persons (other than their beauty & being acclaimed, by fashion-y people, as influential fashion "figures"-- of course way too early to say "icon"). But as young women of not much accomplishment who find themselves acclaimed, for whatever indefinable reason, as "it girls." I think of the young Chloe Sevigny qua "it girl", too-- but as much for the differences as the similarities. I actually remember reading the long-ago New Yorker article about Sevigny when it came out, back in the day-- when she was just a teenage girl hanging around skaters in Washington Square Park (I immediately liked her because she liked Pavement, at the time my favorite band). There too, you had a writer gushing over a girl, trying to articulate something about her "it". In that case, too, she was soon swimming in overlapping circles, with fashion (e.g. MJ grunge period), music (appearing in Sonic Youth videos), and art/film (starting with the Kids movie).
Of course: it all depends what you *make* of "it" (which is so evanescent). Especially now (we're beyond Andy Warhol's 15 minutes, more like 15 seconds). The nature, depth, & extent of Alexa's talent(s) remains to be seen. Edie & Chloe also had more mystery, a deeper kind of allure-- it's one thing to be intimately associated with Andy Warhol, or Harmony Korine, and another to be known for-- hosting cheesy TV shows. And if the MTV show is cheesy too, there's a risk she'll be "branded" by that. But it's also a springboard. If she can act-- I can *totally* see her as perfectly charming in a romantic comedy. (Greg Kinnear started out as the host of Talk Soup.) Or perhaps branching out in the TV hosting gig-- although she's limited (perhaps) by her limited education. Anyway: of course she can fail. On the other hand, it's also a very promising leap. (And seriously, career-wise, she was completely stalled in the UK. T4 & Gok's Fashion Fix or whatever? Time to move on.)
She already has a 'decent', relatively successful career in her chosen field. Should she try a different, more repected career? Only an Arctic Monkeys fan would say she is 'defined by her relationship'; it helped her initially but associating with Alex Turner definately didn't get her Elle or HB covers 
. Not that it's something to be more proud of, but it's her style and good looks that have given her widespread exposure. Ultimately, where she chooses to live and her friends ("useless hipster pals") are her own business. Maybe she just decided she would like to live in New York while she is young and has the opportunity.. I really don't find that hard to believe.
its not exactly any of our business anyway
God forbid she enjoys their company. 
