This is the passage in question:
I miss Kit Kats.
That little chocolate candy with the cookie thing in the middle and it goes snap when you break 'em.
Click, click, click I miss Kit Kats.
Probably a ton of 'em out there, too, just sittin' there in stores.
Might as well be on the other side of the moon all the good it does me in here.
What the speaker is saying is that, in her current situation ("in here"), the stores which have the Kit Kats are as easy to get to as the other side of the moon: in other words, impossible to get to.
This has the opposite meaning to the given translation of "Come to think of it, I'm relieved to be in here". The speaker is in fact unhappy to be there, because it's stopping her from getting a Kit Kat, which she is craving.
So, it's a very bad translation.
On further reading, it seems like the speaker is in some sort of survival shelter, where she (and possibly others) are sealed off from the outside world for their own protection. Earlier in the passage, she reminisces about going to fast food stores with her family, and later in the scene, it appears that some desperate people are trying (fruitlessly) to get in, in order to avoid some sort of terrible fate (eaten by vampires?).
This actually colours the translation a bit. The speaker is presumably relieved to be in there generally speaking: it sounds nicer than whatever happened to the people trying to break in. But in that exact moment where she's craving Kit Kats, the translation doesn't make sense. At that moment she is focussing on one of the aspects of being in there which she doesn't like – that she can't go to a shop whenever she wants.