Is there any possibility that the girl was ethnically Chinese who was raised in Japan? I mean, that happens more frequently than we realize. Because to me, (though my Mandarin knowledge is very, very basic) "Shawn" could sound like names --- Xian, Xiang, Shan, Shen --- depending on the character that her names is written with --- although feminine Chinese are typically build from two characters.
(**-"Xi" is pronounced nearly identical to "Sh" to Western ears... however, there IS a difference to native speakers