Cara didn't ask to be stationed right on top of the Hellmouth. She certainly didn't ask to put her extremely expensive education to use trying to convince a bunch of drooling American teenagers to pay attention to Latin verb conjugations. In fact, she'd strongly prefer to avoid demons, non-Slayer high school students, and other such unsavory creatures altogether. But, well, she's the one who decided to become a Watcher. She made her bed, she has to lie in it.
Of course, when she signed on, she didn't expect a missing Slayer.
The girl seems to have vanished off the face of the earth, which, of course, means demonic activity is skyrocketing. And, of course, Cara's the only one around with even the tiniest chance of keeping it in check. Which is why she's poking around in the boiler room during her lunch break instead of popping another aspirin and taking a nap on her desk.
Whoever this missing Slayer is, she'd better have a damn good explanation.
"Are you threatening - look, I didn't mean to be here, is this your place, I swear I have no idea how I wound up here, I wasn't even casting anything!"
(She hopes against hope that the Bella-shaped-entity doesn't call her bluff).
She is wearing jeans and a T-shirt, although not a T-shirt that the usual Bella owns.
"You're a witch and not a Slayer, aren't you?" she says. "Where did you come from?"
"I said something inadvisable to a demon, and the inadvisable thing I said seems to have given it some sort of power over me. Namely, the power to create a witch version of a friend of mine. You could be a perfectly benign witch version of her. You could also be a hostile entity who's also convincing facsimile of a benign witch version of her. Given the nature of the type of demon I suspect we're dealing with, I'm more inclined to believe the latter, but I'm not sure how to prove it either way."
"You made a wish around a vengeance demon? And it got you me? What the hells did you ask it for? Or is it something more obscure?"
"I didn't know it was a vengeance demon at the time. I still don't know it's a vengeance demon, but that seems the most likely. I wished that my friend could help me with something that required the help of someone magical, and I mentioned that I required the help of a witch, specifically, and not, say, a Slayer."
"I'm a witch, but right now I don't feel very helpful, you are not the most welcoming hostess I've ever met."
"What, you think I expect you to help me? No, thanks, I'm just trying to figure out what's going on while ensuring that all my limbs stay attached to my body," she says. "You appeared in my apartment after I made a wish around a probable-vengeance-demon, I am not a trusting person on the best of days, and I just made an uncharacteristic judgment error that I am not keen to repeat. I'm not feeling particularly welcoming."
"Look - I look like someone you know? Who's named Bella? Why don't you get her to come see if I seem to be - like her?"
Speaking of which, she should probably check to see if Bella's come back to her phone yet. She does that now.
"Sorry, something came up," she says. "An unknown entity who seems to be a witch version of you and looks the part has appeared in my apartment. It's possible she's a harmless copy of you, but it's also possible that she's something more alarming, and the only way I can think of to confirm which is which is to have her talk to you. How quickly can you get here?"
"Uh. Ten minutes. What do you mean 'witch version of me'? Like, I didn't know magic existed till I was called, so something else must be different."
"I haven't asked her detailed questions about her memories or where she came from yet, but I agree, that's a point of interest," she says. "Do you want me to stay on the phone with you? I'd like to start grilling her now, but I can put you on speaker if you want to be part of the conversation."
"I shouldn't phone and drive. Grill away, but be civil, if she is a me and we can't get her home it'd be incredibly inconvenient if you and her couldn't work together."
"...I may have botched that already, I panicked when I found her. I tried my best to explain why I panicked, but I did panic. I can explain in greater detail later, if you need to drive."
"All right." Cara hangs up. She pulls up a chair and sits across the table from possibly-Bella. "Are you willing to answer my questions?"
"If you don't get too personal or - like you're trying to figure out how to kill me or anything, I guess?"
"I'm not going to try to kill you unless you attack me or are otherwise definitively proven to be threatening," she says. (And probably not even then. Even if she managed to hold her own, she doesn't think she could kill someone who looks that much like Bella). "Would asking you how you found out about the existence of magic count as being too personal?"