I'd also like to suggest a good search term for discussions about this: "leaky pipe". The analogy is that the process of getting women into open source is like a pipe with leaky points all along the way. All of the leaks need to be stopped up, and stopping any particular leak (whether it is early childhood influences or sexism at tech conferences) will help more deliver more women to the end of the pipe.
Nobody's saying that there aren't other leaks. There absolutely are. But the ones that the open source community can best address are the ones that are specific to the open source community.
If you are interested in eg. encouraging girls in STEM (science/tech/eng/math) education at early ages, there are many other organisatinos working on that. Many of them take donations, or would welcome your volunteer time.