My tactics might seem cruel to some, but as far as I'm concerned you have to make moves decisively in order to lock down what you want here. I obviously don't know you or this girl first hand, so please take my advice with a grain of salt, but here's what I'd do...
1. Start to mentally prepare for the worst: Sounds like you've already brought up the issue of her being distant in the past and got this "home sick" explanation out of it. I don't buy that, maybe she IS homesick but that's not why she's acting distant. She's chewing on something, most likely the merits of your relationship, and she'll be making a desision soon, best to hope for the best and prepare for the worst.
2. Give her all the space she needs: Be the one to tell her that you don't want to move in together. You can always do this later on if things improve, but you can tell her straight up that she's been acting distant recently, and that living together will make it worse. That'll certainly send the message loud and clear - "hey, I understand your working through some stuff, but while your at it I'm over here on the receiving of your chance of attitude." Simultaneously, if you sense you're the one who's doing all the calling and texting, STOP. She knows your number, let her call you, no matter what.
3. Do that thing Roy thought up about inviting the fam in town to show them around: good one Roy, nice way of getting around the expense of traveling and taking time off, and it'll address the given reason for her distance. She'll think it's sweet, and you can use it as an opportunity to see if her attitude improves.
4 Don't be needy: Look, you can't make another person happy. It's the hardest thing to understand about relationships. All you can do is be the best boyfriend, lover, partner etc you can be, and the rest of it is up to her. Don't smother her with questions, or begin inquiring subtly or directly about this change you notice. You've made it clear that its an issue, let her come around or not. In the meantime, just try to enjoy the time you do spend together and don't put pressure on her or the time you spend with her. Let her work it out on her own.
Good luck, I'd be interested in hearing how things go. Plenty of fish in the sea though, and the fact that it is occupying your mind enough to come out and ask us knuckleheads shows your a good guy who genuinely cares. Hope she finds what she's looking for...
