Bella is hanging out in a Jarvis - the familiar one - handwriting a nonaggression proposal-slash-bribe. Has to be handwritten. Damn fussy demons. At least it's okay for her to conjure rather than personally harvesting the weird ink she's supposed to use.
[I found your alter ego, first, and I want to find out why she's been brain-sucking several hundred people and put a stop to it.]
[I do not have any plans to do anything horrible to you. And I am very, very magical.]
[I just need to know what it is she's up to, so I can see about handling her myself. Why do you turn into her?]
[Why not?] Bella asks. [What can she do? Besides kill or hospitalize a few hundred people. Which needs to stop.]
[How attached are the two of you? How much do I have to worry about you when I'm addressing her?]
[I mean, if she's that much of a package of bad news, are you in trouble if things turn violent, should I try to split you up first, tell me how this works, you appear to be an innocent bystander.]
[I'm not a witch. I'm some other stuff,] says Bella cheerfully. [Glory's from far away? My magic's from farther away. It's a really, really long story.]
[If there's nothing more you want than to get rid of her, you should be all over the possibilities I am offering via fancy offworld magic. Look, how much do you know about demons and so on besides the obsequious kind that do her shopping?]