Oxford's status has just been sealed with a first book: what could be more solid proof of "having arrived" than a New York Times bestseller.
Everything is Perfect When You're a Liar is a collection of scattershot essays, written with the UPPERCASE EXTROVERSION of a teenage girl who's drunk three too many Bacardi Breezers. The book also contains precise stipulations for her funeral. My favourite: that Ryan Gosling and George Clooney should dance her corpse into the room "like Bernie in Weekend at Bernie's".
But the most delicious chapter is titled "Finding Leo", a Hunter S Thompson-style escapade, only instead of a pair of 30-something dudes roving through 60s Vegas, it's two teenage girls let loose in 90s LA - a far more dangerous pairing and unhinged scenario.
Their mission: to find Leonardo DiCaprio and make him Oxford's boyfriend before Titanic turns him into a huge and hence unattainable A-lister.
Oxford at 17 doesn't question her own irresistibility. Dressed in blue velvet trousers, black platform boots "and a velvet tiger-striped top that tied up in the back - (It was the 90s, people)", she and her friend tear around the city getting stoned, dodging cops in a borrowed Mercedes and high-fiving Bill Maher on dance floors.
Predictably, they never find Leo, but their adventures seem far better than meeting him ever could be.
When I meet Oxford in a very hushed library of a smart Manhattan hotel, she shakes my hand tentatively and speaks softly. It turns out she's rather shy, with a sly naughtiness that makes her seem younger than 35.
"I can write funny quips, but I'm not a comedian at all," she explains. So in a social situation she doesn't tell jokes? "No, I totally don't. I've never done stand-up; I don't think I could do it in a million years. Writing online," she says, "was just the thing I did when my kids weren't interested in playing with me."
Her writing career has ascended - and continues to ascend - with all the effort and premeditation of a tweet. I believe her when she says she never imagined that cracking jokes online would lead to all this.
"I think forcing things is the worst thing you can do for your career," she says. "I think if I'd tried to become a screenwriter I would have been a failure. I would have spent all this time writing this shitty material instead of learning how to write."
Oxford's success may seem easily won but, in fact, she's been writing for years. She was an "early adopter" - writing online in those quaint days of AOL chat rooms and GeoCities sites that characterised the internet's infancy. By the time Twitter arrived in 2006, she'd already built an audience of about 10,000 through her blog.
At first she was sceptical.
"It was just another website," Oxford says. She took until March 2009 to sign up. "It didn't seem it could be super huge, but I knew I could use it - the format was the same as a Facebook status. Those were always most interesting when they were funny, so I thought: 'Oh I'll just make them one-liners."'
Most of them were observations on family life ("One thing I will never do for my son is correct him when he says 'pervalised' instead of 'paralysed"') and she decided early on to have "no filter".
It's a phrase she uses repeatedly; it seems to be as much life philosophy as Twitter style sheet.
"I realised," she explains, "that I was entertaining people more when I was letting it go."
The writer and director Diablo Cody was one of the first high-profile figures to champion her online, and after that Hollywood comedians started following her. As the retweets rolled in, her follower count swelled.
Just a year after joining Twitter she was invited to Los Angeles to take part in Night of 140 Tweets, a benefit for Haiti where she was the only non-comedian, actor or working writer.
Then Will & Grace producer Jhoni Marchinko encouraged her to write a spec script on the strength of her Twitter feed. "It didn't really mean that much to me," Oxford says.
She'd been interested in screenwriting but "wasn't actively seeking it. I knew how to do it, but I was like: Oh no, I'm at home with kids, writing a blog, that's what I'm doing." When she sold her first TV pilot to CBS, though, "I was like: Oh, this is real."
Last year she sold a screenplay called Son of a Bitch to Warner Brothers for a rumoured six figures.
Now, Oxford says, "every single thing I write is going to be bought by somebody because there are so many different studios and TV networks and they're just like: Oh, I want the Kelly Oxford project."
Her follower count is now at about half a million and a lot of those famous followers have become famous friends. She now hangs out with Lena Dunham, Mindy Kaling, Kristen Bell, Jimmy Kimmel, et al in the real, offline world, too. Or rather the not-quite-real world that is Hollywood.
The Oxford family relocated to LA last summer, and she and her husband have effectively swapped roles; he left his job as an environmental engineer and is now a stay-at-home-dad while she works full-time.
Their eldest daughter, Salinger, is 11, their youngest, Beatrix, is 3. And then there's 9-year-old Henry, who, she says, "has a teacher that he hates so much and now he's miserable going to school".
This is exactly where Oxford is able to flaunt an unusual mum-superpower. She smiles: "I told him: 'For the next pilot I write, your teacher is going to be a character in the show.' So now he goes to school and he brings me home all this material. Little does she know I'm going to use all of it!"
"I was totally unembarrassable," she says. "I think I still am. What's acceptable and what's not acceptable is basically what's going to hurt somebody. That's the only filter and that's a natural filter by the time you're an adult.
"There are people who deserve criticism. Like the Kardashians. But only because they're not honest about what they're doing! If they went out and straight-up said: 'Yo, all this is happening because I made a porn tape - I don't really have talent', people would embrace them! It's just the falsity."
Oxford's all-honesty philosophy includes not having a publicist. "And I'm not going to, ever," she says, "because I've done everything so far on my own, and it's worked."
There are no doubt thousands of Twitter users now attempting to model careers after hers. Oxford is the prototype of a new kind of celebrity, by which anyone who just happens to be very funny in the 140-character form can push themselves famewards one tweet at a time.
Everything is Perfect When You're a Liar by Kelly Oxford is published by HarperCollins.
