1) By increasing TURNOVER in the bottom 10%, both the weight gain and the psychological stress causing it would be spread among more girls and thus cause less harm to any one individual, and not implausibly less aggregate harm;

2) If the actual cause is perception of status like your executive summary of the article suggests, a program that ‘lifts all boats’ may cause an overoptimistic appraisal that more or less halts the bad effects of RELATIVELY low status entirely (compare the number of people in the US who think they’re in the top 20% of incomes with the number who actually are);

3) If a program to teach social skills actually works (admittedly a big if) then it is likely to be in itself a much bigger objective good to the students in question than any weight loss it may or may not produce.