Nothing against educating girls, but this is probably the wrong conclusion. Economic situation determines whether girls can get an education or not, so educated girls correlate with a good economic situation. Not the other way round (educated girls causing a good economic situation).
Personally, I think this focus on girls only is sexist and I take care to never donate to charities that only want to help girls.
I think in areas with more traditional cultures, educating girls DOES improve the situation over a longer time horizon.
Those girls will become mothers, and their education will translate to providing better opportunities and a more sophisticated outlook for their children.
I agree it seems sexist to only help girls, but helping anyone is good.
Personally, I think this focus on girls only is sexist and I take care to never donate to charities that only want to help girls.