That's...concerning...is any of the hell-writing anything more useful than, like, "somebody save me."

There's a lot of "why". There's a lot of attempts to count days. There's a lot of people writing their own names over and over, or the names of their loved ones, or snatches of poetry. Sometimes there are messages for later arrivals--"fewer demons that way", "beware: ants", "even despair has an end". Nothing that looks like anyone expected a living person to read it.

Wow. Hoo boy. They're gonna need to import so many therapists. Not that she didn't realize that, but. "Even despair has an end" is definitely extra concerning. 

If she's going to deploy conventional explosives against God (why the fuck is that even a thing that might work) with minimal damage to innocent bystanders...is there anything published about, like, the layout of Heaven. 

There is! Prophets have had visions of Heaven, and theologians have pieced them together into some fairly complete maps. Like Hell, Heaven is a finite space in the shape of a cylinder. It has nine levels, arranged vertically: the region where the saved dwell in bliss, seven levels occupied by the seven angelic choirs, and then God's throne at the top. Each layer is immediately recognizable by its inhabitants; unlike the diversity of forms seen in demons, each kind of angel is pretty similar to the others of that kind, and they're all different kinds of extremely weird-looking, starting with six-winged humanoids and going from there.

...If it is a finite space how does it fit all the souls. 

It's a pretty big finite space and there's only ever been a finite number of people. There's a theological debate about whether it gets bigger as more people die or just gets more densely populated. It's fairly dense in at least some areas, but since there aren't any buildings and the saved just stand in one place singing songs of praise to God this doesn't really complicate things much.

That is all they do. Thaaat's creepy. 

"Your world's god is so fucked up."

People who are confident they're saved usually talk about Heaven like they expect it to be wonderful, but. Bruce remembers being very small, four or five, and asking if there were dogs in Heaven, and being told that eternal bliss was better than having a dog. He didn't totally buy it, even then.

"Yeah. Pretty much."

"I apologize for him on behalf of divinity in general and Jesus-flavored divinity in particular." 

"Um, apology accepted but also it's super not your fault?"

"It's not my fault but it is--if someone looked at this and then looked at me and went, 'ugh, you're a Christ?' then they wouldn't be out of line, you know? --It's not my fault but it is my responsibility."

"That's--really reasonable of you? Not that it matters whether I think you're being reasonable or not. Obviously."

"I think it matters." 

Bruce keeps getting these statements he doesn't know what to do with, and every time he tries to do something with them he gets another one. Maybe instead he can just stare at his own feet for a bit.

"What else do you need to know before you can--do what you're planning to do?"

She bites her lip. "I think I'm going to spend a little more time seeing if I can get anything useful from your world's literature just in case, and then I'm going to go into your world, teleport to your world's God, and conjure a little bit of antimatter."

"Good luck. I hope you and everyone else end up okay."

Sigh. "That's always the hope." 

Flip flip flip no last-minute revelations?

Unless the Book of Revelation counts, no.

Is the Book of Revelation interestingly different from her own?

Not especially. It's maybe slightly more lucidly written, but the events of the prophesied End of Days are the same.

Well, there's not going to be an End of Days if she has anything to say about it. 

"I'm ready," she tells Bruce. 

Bruce is aware that however this turns out it will be an important moment in history. Hopefully if someone writes a book about it they'll leave him out of it. Hopefully enough people will live to remember this that that's a concern.

He says solemnly, "Good luck," and opens the door.

She steps through

and teleports to where God is

and conjures several grams of antimatter. 

As soon as God realizes there's an intruder in Heaven, he throws a massive amount of lightning. But the matter-antimatter explosion is already flooding the area with energy. 

God can handle energy. The spacetime of Heaven, already under strain, cannot. Reality starts to tear and fold into isolated islands like a pot of soapy water getting stirred into foam.

Christina might want to find somewhere else to be before the place she's standing stops being a place.

She jumps back to earth and re-corporealizes herself and decides to wait a minute before doing anything else in case something makes itself known to her in that time.