Charlie's well-established as a geek, a nerd, an enthusiast, whatever you want to call it. Accepting that some of those things aren't as fictional as she thought - not so hard to do. She adjusted pretty quick, given the amount of horror and violence involved in her first exposure to the supernatural.
Some things - the monsters, mostly - were really easy to wrap her head around. She'd seen all the movies, read a lot of the books; once someone taught her the rules for these guys, the things to say and carry and wield, she was okay. And hey, it turned out nonlethal monster girls were easy. That was an unexpected bonus.
Other things took her a while to realize were even a thing, you know? Like, Charlie's had her share of relationships, maybe slightly more than her share of one night stands. Whatever, the existence of an acceptable maximum or minimum number of partners is bullshit, she's sex-positive enough to know that. Point is, Charlie? Definitely not a virgin. But you wouldn't think it, the way supernatural things went.
Like, the coven of witches that tried to make her the virgin sacrifice in their demonic ritual? She could pass that off as most of the witches being sixteen or younger, and tricked into performing the ritual by the oldest two. They really hadn't known any better, and not just about virginity. She'd basically given them a full sex ed talk while she waited for Sam and Dean to come dispose of the demon-possessed witches.
So that had been weird. But then, later, she'd been doing tech support at the Men of Letters bunker for her favorite pair of idiots while they were in the middle of some spell to reverse some curse on some thing. Charlie obviously hadn't been paying much attention. Dean asked her for a fingerprick's worth of blood, and assuming that he would've told her if it was going to pass the curse on to her or whatever she stuck out her non-dominant hand and kept typing. Her finger hurt for a second, but then the blood was in the bowl, words were chanted, sparks flew, and the curse on the thing was gone.
Sam frowned at Dean after, the whole force of his forehead behind it. "That was really risky, Dean," he chided. Dean scoffed. "You didn't know for sure if Charlie's blood would work - "
"Sure I did," Dean said, waving Sam's concern off. "If she would've counted for a witch ritual, she'd count for this."
Charlie was suddenly more interested. "I'm sorry, what might I not have counted for?"
Sam sighed. "The spell asked for a drop of blood from a virgin."
"Which... I am not?" Charlie wrinkled her nose at the bowl of stuff and the now uncursed thing. "But it still worked."
"Yeah," Sam said, frowning at the bowl like he was disappointed in it. "We don't really know why."
"Magic," Dean said with a shrug and jazz hands, like that explained everything. It didn't, but after taking advantage of the bunker's resources and doing a little research of her own, Charlie found out that there really wasn't an explanation. It was just... the done thing, magically. Sex only counted if it was p-in-v. Very heteronormative, she thought grumpily, but it was a centuries old establishment primarily founded by white dudes, on the topic of female sexuality; what was she supposed to expect?
So, even though she didn't like it, she accepted it: by magical rules, Charlie was considered a virgin.
(Magical rules were stupid.)
It was good timing on her part that she came to that conclusion before the last, best virginity encounter, a.k.a. the unicorn, a.k.a. the greatest selfie she'd ever taken that could never be posted online. If she hadn't accepted it, had been willing to argue against it, the unicorn might've not let her get close enough to pet and pose with. And that would've been a tragedy.
"You know," Dean said slyly from the edge of the clearing (the closest the unicorn would let a guy get before goring him, they'd discovered), "I could tell the unicorn the truth."
"Huzziwhanow?" Charlie asked. She was a little dazed by the glitter and the shiny and the soft, soft fur. "What truth?"
"It's just, I know how much it bugs you when magic and monsters and stuff think you're a..." He mouthed the word 'virgin' slowly. "When you aren't one."
"No, noooo, no no no." Charlie clung to the unicorn's neck. "Don't do that, please don't do that, Dean. That would be so mean, Dean." She pouted a little, and made her eyes wide and watery. Between her expression and the unicorn's, Dean backed away. And yeah, sure, it turned out the unicorn was kinda sorta accidentally inadvertently drugging her to keep her nearby and cuddly, but no harm no foul, and in retrospect it had been a damn good high.
The unicorn glitter that kept falling out of her hair for the next few days was a little annoying, but if that was the worst thing that happened to her because magical things stupidly thought she was a virgin...
Well, Charlie would be just fine with that.