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.
"Dude," says Bella, pinching the bridge of her nose, "I told you, multiple times, I don't know if I can do it till I try it. I can do all kinds of wild things, but neither I nor my friends have encountered the specific scenario of 'hell god possessing human' before. And I'm trying to find out whether you can live through it, so that if the answer is 'no', I can find another solution. You aren't helping with the 'find out' project, so I'm trying to explain why it is important and you should wish to be helpful. That doesn't mean that I'm going to charge blindly forward in the absence of the relevant information."
"Offworld magic," sighs Bella, looking skyward. "There are lots of worlds, you know that already 'cause Glory's from one, but Glory's from one in the same collection as this one we're standing in. I got some magic from some friends who are from other world-collections. What else do you want to know about it?"
"Wishes. I have some wishes on my person, of various sizes, and I can spend them at will."
"Think of the wishes as magical computer programs," Bella says. "If I wish 'unstick Glory from Ben, put Glory on Mercury', then this will either work or not, but if it works, something I haven't thought of could cause something I don't expect, just like computers don't always behave even though no one expressly programmed in any bugs. That's why I have to think of all the things that might go wrong first. What will Glory be able to do when she's unstuck? How fast will she be able to do it - faster than I can stop her? Are you, in some way you have not chosen to tell me about, attached to her in such a way that you will come to harm in her absence if I don't specifically wish around it? I know some people whose lives are dependent on external souls that are shaped like animals, it would not be the weirdest thing I've heard if your life is in some way dependent on Glory's occupancy and I can probably work around it but I have to know how to be sure."
"And I'm telling you, I can potentially use anything you know about her at all in order to find out. I have other sources of information too, I just need to know what to look for."
"I have a research guy who's investigating assorted books. I can spy on the past, if I know when and where I want to look. I have a crystal ball, but I have to interpret what it shows me in light of whatever I already know. I can wish up other information-gathering abilities if I know what sorts of things I need to find out."
"Okay," she sighs, since this is not a lie. "In the meantime - I can precipitate shifts between you and her, I did this most recent one. Would you expect anything bad to happen if I pushed you out front more often?"
"You don't think it'd make her hungrier for human brains, more pissed off, anything like that?"
"Okay. I guess I'll take you back where I got you now, then, unless there's anything else you'd like to tell me."
"Here we go. I guess I'll see you when I work out a plan or she's about to hurt someone and I have to go with whatever I've got at the time, huh?"
She heads back to Canada, although she half-suspects Sherlock will have teleported Soph to a more habitable climate by now.