Goji: That's so awful! I have to agree with what the other posters have said thus far. This girl may definitely have mental illness, such as bipolar disorder or depression and if that's the case, then she can indeed turn a 180 on you for no apparant reason. I'm really sorry that this has happened to you. I must warn you that the Japanese don't like interracial relationships at all so the mother could hold a grudge against you in that sense.
What I would do is attempt to contact the girl and get her side of the story before you jump to any conclusions at the moment. Maybe the mother is psychotic or something and doesn't want you around her daughter? A lot of mothers are very overprotective of their children and sometimes have a tough time letting them go. I'm not for sure since I don't know them personally but
I do agree that you need to contact the girl again and get her side of things first. I just hope that this isn't such a finality to you..because if it is, then you'll probably be emotionally scarred for a while. I hate it that this happened to you! You feel like you've met "the one" and then she's ripped away from you for no apparant reason. That really sucks, man!