Cassie is, first and foremost, a realist. It's why she sends Dean away when she finds out he's utterly insane. It's why she calls him when she realizes maybe he isn't. It's why she sends him away again when she learns that yeah, he really is, even if not in the way she thought at first.
It's why she quits her job and hits the road. She doesn't have the nerve to hunt the things that go bump in the night, she knows, but now she knows how to defend herself from ghosts (the single most common flavor of nasty supernatural shit, Dean informed her), and it's her duty as a journalist to make sure that knowledge gets disseminated as widely as possible. Even if everything she writes gets a much better reception when advertised as fiction framed as journalism than as actual journalism.
Even if she wakes up every morning absolutely convinced that she took the fantastic path, not the realistic; even if, most of those mornings, she means 'fantastic' in the original sense, not the popular, and takes 'realistic' to mean what it would have before Dean, not after.
Reality is that which, when one stops believing in it, fails to go away. Case in point, hate-crime-committing ghost trucks. Besides, there are more important things than her job security.
She doesn't call Dean again. She doesn't have the nerve.
It doesn't take long before Cassie's adept at recognizing the signs of a supernatural attack: disappearances from upper-story apartments locked from the inside, back-to-back murders identical save the names of the suspects and victims, an unusually high number of fatal accidents on the same stretch of road and the same day of the year. She documents every instance, every death and near-miss, interviews everyone who both knows anything about the incidents and is willing to talk to her. She starts formulating theories about Dean and Sam's...colleagues, she decides. Most of the people she's identified as hunters appear only once in her file, or more than once but in the same corner of the country (Sarah in New England, Kat near the Great Lakes), or have such vague descriptions that she has no idea whether she has one early-twenties white blonde female hunter on a road trip or a dozen such hunters with home territories. There's a handful who turn up everywhere, and then there's Dean and Sam Winchester.
And then she's researching a series of deaths every few years going back to the fifties, points of commonality among the victims being (1) female, seventeen, dark-skinned, about five-nine (2) student at a particular high school (3) found stabbed the morning after the prom she didn't attend. The 'fifty-six victim was the only one where anyone found a weapon, the only one with more than one corpse (murder-suicide), and Cassie's ninety-five percent certain her ghost is 'fifty-six girl's dumped prom date (and a hundred percent certain that a not-insignificant number of seventeen-year-old black or brown girls have been coerced into trading sexual favors for safety from the school ghost) when she realizes her data has a significant omission.
Cassie goes over everything again, and the gap doesn't fill itself. She picks up the phone and discovers Dean's number is no longer in service. She never got Sam's, and she's never come into contact with any of the hunters whose stories she's collecting, collating, editing for identifying detail, and selling for pocket change—after the news about Dean's stunt in the bank in Milwaukee, she knows Dean and Sam are trying to stay under the radar, which she's fairly certain is something all hunters have in common, and in any event she's not at all sure any of them would think favorably of her or of what she's doing with what she learns.
The reality of the situation is that odds are better than even that if no one kills this ghost, it'll kill another girl. The reality of the situation is that no hunter has ever been through this town, and there's no way of telling whether any hunter has caught the scent. The reality of the situation is that prom is in a month.
Holy mother of fucking shit, Cassie thinks, I'm it.
She buys kosher salt, lighter fluid, a shovel, and an iron poker. She sneaks into the cemetery as soon after dark as she thinks she can get away with it, pours out an entire box of salt in a careful circle around the grave, keeps the poker in easy reach, and starts digging. It's not prom night, she thinks; I don't fit the profile, she thinks; I'll be fine, she thinks.
No wonder Dean's got so much muscle, she thinks a few hours later. He does this all the time.
The ghost comes after her around three. She whacks it with the shovel, then when that doesn't work tries the poker, and it vanishes. She knows that doesn't mean it's gone. She's been digging since ten and is thoroughly exhausted and the grave's only half dug, but somehow she finds the strength to finish, to avoid vomiting when she breaks into the coffin, to cover the corpse in salt and lighter fluid and to light a match, to sit on one of the piles of dirt and watch the bones burn. She even manages to get a lot of the dirt back in the hole before the sky starts to lighten and she has to run.
Holy mother of fucking shit, Cassie thinks, I did it.
Then she gets back to her motel room and vomits and passes out, and wakes up after dusk and gets herself cleaned up and goes out and gets very drunk and comes back and repeats the vomiting and passing out routine.
The second time she wakes up with her head on porcelain, Cassie decides: she is no more a hunter than a war correspondent is a soldier. It's not where her talents lie, and she doesn't have the stomach for it. But she is going to continue to bear witness to these heroes and she is going to continue to do her best to educate the public on what it's really like on these battlefields, and she is damn well going to put on some muscle. There are more important things than her delicate constitution, and when the situation requires it, apparently she does have the nerve.