Academic psychologists are mostly female. That would seem to be a pretty good target audience for LW. There are a few other academic areas that are mostly female now, but keep in mind that many academic fields are still mostly male even though most new undergraduates are female in the area.
There are lists online of academic specialty by average GRE scores. Averaging the verbal and quantitative scores, and then determining which majority-female discipline has the highest average would probably get you close to your answer.
but keep in mind that many academic fields are still mostly male even though most new undergraduates are female in the area
Well, keep in mind that 75% of LWers are under 31 anyway, so it's the sex ratio among the younger cohorts you mainly care about, not the sex ratio overall.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.