Puff,
I just read this whole thread and it does seem that everyone has laid it out and IMO is pretty on it with what is really going on. I am just going to give you some advice because I have gone through this before and think that if you give her the option it will end badly for you. If I were you I would tell her straight up that if she is leaving that this is a break up and not space for you. As you said marriage should not be like that, someone you marry you should not need space from IMO. Don't threaten her with it though, but be firm in your position. Also, make sure you look at ID's bro!! Your at that magical age where the young girls still want you because you provide the means to do everything they want at that age, you're basically a facilitator to their enjoyment.
I'm not sure of the Statutory laws in Canada but in the states what you and I (I was 21 and she was lying about being 16) have done is a crime, even if you didn't know she was a minor. I was fortunate in that the woman I was with I married (DIVORCED NOW) and escaped the laws, but it could have been a real issue. And remember she lied to you from the beginning about her age and probably many things in her life so always consider this as well.
Now, in her defense make sure you're not being over-bearing by forcing the issue of school or pressuring her too much into finding a job as this can make it even harder. Sometimes the pressure of the move and those things combined can make anyone home sick and depressed. The weekend trip together to visit back home is a good idea, or go spend some time rekindling the relationship somewhere if your set on trying to make it work. Personally I would end it now and start the search for a new partner in crime, one that supports your canna use and if the girl your with now fights to keep you well then maybe we were all wrong. Good luck with everything and I wish you the best, you're young so don't set your aim too low.
KnB