This is just me, but I think it's a good thing that BTW sales in the US is not too high now, but still stable, so that people will most likely still buy her singles. We all know worldwide success is more important, but when we talk about songs' peaks, it's all about Billboard Hot 100.
And her worldwide sales is good now, and BTW can reach 7 millions by the end of the year, so we have nothing to worry about.
Again, this is just my opinion.