Not many, sadly... My friends already like Japanese music, and either they don't like her genres/voice/style, or they're already fans.
One of my closest friend (and my fellow karaoke-partner) used to like her without really knowing any songs. Basically, the ones she knows and likes now are the ones I do at karaoke: Kabukichou no joou, Tsumi to batsu, Marunouchi, Gibs, Honnou... She bought her first album not too long ago: SS
Thing is, our SR karaoke selection is pretty limited, but I think the next breakthrough should be Yattsuke Shigoto!
Another of my friends likes a lot of different stuff (usually more on the pop side though) and the only SR/TJ songs he likes are Killer Tune, Kono yo no kagiri and Gibs. And he swears he once downloaded her entire discography and those were the only ones he liked. I seriously doubt him on that.