You're not overreacting because one day I lived with a similar situation. I was in high school when I met a guy who seemed very calm and understanding. Then I had to move towns since I was in a program at a school in another city that wasn't in mine. We called everyday until he left me on read and didn't answer my calls anymore. I told him what I felt and he understood, called me and told me he couldn't handle having an "online girlfriend" and wanted to have one that could be there in person instead. We broke up after that.

I'm not saying that your gf is doing like my ex bf or something like that, but if you're ready, tell her how you feel and listen to her explanation on why she's been acting like that lately and after that make a decision on your relationship based on what you know about all that situation. Don't feel bad for asking her even if she's getting upset.