"I think the effort has to start before college. "
@intparent is right. So here is an observation from my D’s elite public high school. In the most advanced Physics class the school offers to seniors, there are 3 (count 'em) 3 women in a class of 24 kids. This is in a district that runs a STEM accelerator in middle school where the most science-oriented kids are tracked into classes with extra low student:teacher ratios, advanced math, extra hands-on science lab work, and encouragement to participate in science extracurricular activities (e.g., Science Olympiad). Then they get tracked into an appropriate high school curriculum.
So, what happened to the pipeline of these STEM kids between middle school and the end of high school? For the answer, all you need to do is to show up at the regional science research competition. County-wide, there are about 400 kids in my D’s class (across all the high schools in the county) who are involved with independent science research. Yet only a dozen of these kids are doing topics related to physics or engineering. I know; I counted. The vast, vast majority of these kids are doing some sort of pre-med related science research.
So the issue isn’t whether the top LACs are doing enough to attract the best and brightest female math and physical science students. The issue is that there just are not very many of these students to begin with. There could not be a more illustrative test case of what is actually going on than my D’s school district. There are no unmet academic needs in this district. Top paid faculty and administration in the country. And we produced 3 (count 'em) 3 women in the top-end physics course in 2017.