To be honest I don't think she actually needs the CBB promotional boost to "revive a flagging career". It looks more like it is a "nice to have " from her point of view. I was quite surprised to learn that she does indeed have a significant fan base in the world beyond the UK.
It may come as a shock but there are 6.9 billion people out there buying records that do not feed into the stats of the UK top 40. Success in music does not begin and end with our anglo-centric charts. There are plenty of mega successful artists out there that most of us will have never heard of.
Astonishingly she has made 7 albums (plus two greatest hitsalbums). Few artists get the chance to make a new album if the last one didn't sell, so it suggests that she is selling albums. It seems her world wide album sales over 20 years amount to 30 million copies sold.
It also seems she can sell out 20 and 30 thousand seater concerts. In fact she did 3 nights at 70,000 seats per night in India. A UK chart success I am sure would be a feather in her cap but even if it doesn't happen I think I could live with Sam's "lack of success". Her career seems pretty healthy by any sane measure.