I think the problem she's pointing out is that the stereotype sets up a false ceiling for girls. Under the stereotype, if a girl achieves as high as a boy, the boy can just put in more effort but the girl is maxed out.
Praising the effort over ability is important as so many researchers point out. Praising a girl's ability would seem to be a solution to overcoming the stereotype but it creates more problems than it solves. So my working theory is: praise the girl for her effort but make sure teachers are aware of her ability too.
