Her sales aren't pretty bad, she is always in the top 50 (forget some singles from VoE era)
She isn't a super seller, but her sales are ok, she is not flopping a lot and she isn't out of the top 100 of Oricon.
And anyway, if she ends her career in Japan, she is gonna keep in China, but probably without Kazuhito and his excellent songs.
I tell you guys, don't worry about that, enjoy her music and support her please, she needs a lot of our help !
Sorry for my english .....