I know you meant your comment as sarcasm, but to do it, you need to have a legacy worth those kind of numbers to begin with, instead of selling your labor as most of us here do. It's not so different that celebrities associating themselves with brands through advertising.
And as distasteful as it seems to many of us, people like her spend years building their social networks and a reputation for various personality and behavioral traits in a boardroom.
Also, I doubt her legacy is closed at this point. The traditional next step would be to write a book based on her career capped off by her experiences at Twitter.
There's maybe a small percentage of the population addicted to buying brands beyond what they could possibly use, but most people run out of the ability to buy a significant amount of stuff every year. I.e. even a thousand a month habit is insane to maintain and nothing compared to bad housing choices.