There are a lot of armed and uniformed men and women inside! Many of them are now pointing said weapons at her. One in the back seems to be whispering a description of her into a communications device.

"Identity yourself," demands someone who may be an officer, judging from the insignia on the shoulder.

"Green Lantern 2814. Got shot through a portal just now and I'm very confused."

It's cool that her costume has a facemask, because she might just have to make herself scarce in a bit if this goes really really wrong.

"...says she's green lantern? No sir. She is green, sir. Glowing. Yes, sir."

"This is an active warzone. Who authorized your presence here?"

"Literally no one, I got shot through a portal about three minutes ago and this is where I got spit out? I did notice the warzone thing, I understand that this is a really bad time for you. If it would be better for me to leave then I can do that, you just looked like you might plausibly need some help on the not all dying front? I am a fan of people not dying."

The officer looks skeptical. "Corporal?" he calls over his shoulder.

"Inbound, sir. ETA-"

A streak of golden light interrupts the corporal's report and there is abruptly a girl in a sparkly dress standing between the soldiers and the Green Lantern.

"Hi everyone. What's going on?"

"I got shot through a portal!" she says, helpfully. "I'm wondering if there's anything I can do to help, but your people are understandably very concerned about the sudden unexplained interloper. That's about it on this end, I'm pretty lost. Sorry for diverting resources from the primary matter at hand, wasn't intentional."

"Yeah so when a strange magical girl shows up that's usually not a good thing. How about you and me hop a couple buildings over to talk so the sergeant can relax a bit."

"Sure thing," she says, and flies to one of the skyscrapers that she's pretty sure is abandoned.

Anneia follows, taking the distance in several great leaps, bouncing off the sides of buildings.

"So you said something about a portal? Where are you from?"

Hmmm. Assuming that supers are as thick on the ground here as they are at home, and assuming that they're as varied as they are at home, sometimes with access to honest-to-goodness magic, and carefully not making any assumptions about whether the person she's talking to is generally on the up and up, and knowing that a bunch of people are going to die if they somehow get to Earth and invade, even given the Justice League's obvious ability to oppose them -

Oa can handle itself, surely.

"The Green Lanterns are based on a planet called Oa. We're a peacekeeping force that spans the galaxy, so we get called in to deal with anyone similarly powerful who wants to make trouble. Unfortunately, the troublemaker of the day has a portal gun, and apparently he can send people pretty far away from where he is. I'm gonna try to get home after this, obviously, but I'm not in such a rush that I can't stop for anything." 

"Uh, yeah, so there's no planet called Oa or Green Lanterns in this galaxy."

"Officially pretty concerned about the strength of that portal gun, then."

"We don't have anything like that, either."

"Oh, the portal gun is new, that's no surprise. Green Lanterns are fairly structurally normal, though, I expect that wherever we are is far outside Oan territory."

"I mean, unless half the galaxy is 'far outside Oan territory' I think you might be from another dimension or something." Or just actually insane but that wouldn't be productive to say. And there's the weird mask and the weird costume and the weird green glow and all that together adds up to a whole lot of weird.

"That's possible. Might honestly have been easier than transporting me a couple galaxies over, though I've heard of both things happening. Ohh, I know," she says, and gives a mental command to her ring. "This is - yep, nope, comms are dead. Different dimension or profound interference it is."

"Okay, cool. So now that we've established you're not a whitesider here to break our trap before we can spring it, do you mind if we walk and talk? 'Cause the tanks'll be rolling in in about five minutes and I was supposed to snap their line about fifteen blocks north of here."

"Fine with me."

"Great." She hops down to the street and sets off at a quick run.

Karen flies, though she flies very close to the ground. Flying is easier.

"Isn't that a waste of power?"

"Fairly negligible. If I wanted to turn the tide of this battle by myself I would have to run some serious calculations, but I'm pretty sure that trying to win a war that you know literally nothing about is against one of the cardinal rules of diplomacy anyway."

It would be worth thinking about if she didn't have her backpack on her and her lantern in the pack, but luckily her past self has done her a solid here.

"Huh." Okay, yep, running on different rules. "Well, it's not like you could actually win the war from here. It's just one planet. And the Compact doesn't care much about it or the assault would have more magical support than that girl down south. Of course, the Domain doesn't much care either or it'd be more than me and Cia."

"Sounds like a depressing state of affairs. You'd think they'd try to take places of strategic importance, but I guess it's different when you're dealing with a war spanning, what, your entire galaxy?"