I have been dating a Japanese girl for over a year now but in December she graduated from the university we both go to, so she has to go back to Japan.
I just don't know if she is willing to get married so soon.
My question is, if we do get married, does she lose or Japanese citizenship if she wants to stay in America for a few years while she works?
You're asking the wrong question.
Here are some questions to ask yourself:
"Why would I marry someone I've only known for a year?"
"Is she willing to marry me? Why?"
"Do we understand the concept of marriage?"
"What's more important to me.....my life six months from now, or my life six years from now?"
And I've got a question for you: have you ever met anyone in her family or experienced first-hand what her life was like before moving to America? I'm not saying you shouldn't trust her, but I'm curious if all you know about her life in Japan is based upon what she tells you.