A novel idea, but have you thought about talking to her about your relationship?
I don't think you're reading too much into things. Any time you notice changes in a relationship, it's worth being concerned about. If you detected a shift, I think it's good to question it. I'd recommend talking it over with her, though, rather than making assumptions.
As for getting over homesickness, distractions could work; keep her busy. If your phone plan doesn't allow for unlimited calls home, you may look into that. Also, she should invite her family up there, and show them around the city.
Ultimately, though, if Boston just isn't for her (and it's not for everyone) you're going to be faced with some life decisions.
Also, I know this isn't what you want to hear, but if you're experiencing distance in the relationship, I'm not sure this is the time to move in together.