I just read your issue which just sounds like what my bf said b4 we go out.
usually Japanese females are nice and like to help a person who is trying to learn Japanese outside of Japan but it is not hard to see if a girl likes you or not.
my bf also mentions, i always gave him polite smile while i was teaching him english, could not tell how I really feel. he actually asked me for being a relationship a month b4 i go back to Japan (yes, he was also afraid) it seems like you guys dont have enough time either... so you should better go for it as soon as possible.
n come on if she does not like you that will prove that she is not THE ONE.
gambatte!
fyi, im japanese and my bf is american