I think one about women in STEM is that often, we don't really know what jobs are available. Yes, we know what nurses, doctors, vets and teachers do. A lot of people have an idea of what engineers do, at least on one level And you can take a guess at some things like research scientist, but most of the people outside the relevant fields won't have more than a vague idea, and when it comes down to some jobs like UX designer or unix admin and various other tech roles, most people outside of IT have virtually no idea at all. So if parents don't have any idea about jobs involved, they're not going to talk to their children about them.
On top of this, we don't tend to see many depictions of STEM jobs in soap operas and so on. We see the IT Crowd and The Big Bang Theory, which are mostly nerdy men as a figure of fun. Where's the working mother in a soap opera, who happens to work in user experience testing or is a lab technician? I suppose part of it is that having people work in customer facing roles (receptionist, bar work, catering, retail,) opens up more opportunities for moving stories forward and interaction with other characters, which isn't so easy with a pass-accessed office or lab. So other than medical staff and mechanics, we tend not to see STEM roles as a just by-the-way, incidental part of everyday life.
Nonetheless, there are girls who make it through school without dropping STEM subjects - this is more likely to happen in single-sex schools. Some make it through university, too. I think another issue is that our education specialises way too early in the UK - I think the Scottish highers take a wider range than at A-level, but nonetheless, we do force people to reduce their choices at a ridiculously young age. Many people have no idea what they will want to do when they're 14 and choosing GCSE subjects, but those choices may be cutting people out of studying STEM subjects at higher levels even at that age.
Nevertheless, she persisted, and some girls do end up working in STEM. I was at a women in tech event a few years ago, and one of the speakers said, "You tend to get a certain sort of woman working in computing, because the rest don't make it." You do need a thick skin and certain level of stubbornness. I met someone who worked in nuclear physics, and she said she won't get involved in any events promoting STEM to girls, because she doesn't want to have the guilt of encouraging them into an environment which is still sexist. It's rarely overtly sexist these days (though don't be under any illusion that doesn't still happen), and a lot of men seem to think that as long as they aren't actively groping anyone by the photocopier, they're doing their bit, and everything is fine with the culture.
It's not though. There's plenty of unconscious bias (and at times, conscious bias.) Just happens to be the man who gets the promotion and that high-profile project - again. Happens rather too often to believe it's all fair and based on merit.
Then you get to a point where maternity leave or redundancy or something forces you to take stock of your world, and you realise you don't want to have to put up with that crap every day, you don't want to have to fight for everything in a way your male colleagues don't need to do. So you decide to go and do something else where you can focus all your energy on actual work, rather than fighting the system just to stay level.
And so the other women who made it through, 10, 15, 20 years behind you - they don't see any female role models in their area. All the managers are men. You find it difficult to believe that women can make it there, and meanwhile, all the male managers will be bemoaning that they can't get any women, despite all the gender equality initiatives they have tried. They will see there is no sexism, because it doesn't affect them at all, so they just don't notice all the institutional bias, and they'll decide that it's all because women just don't want to do it, so it's not their fault, and they don't need to change.
It can be very, very tiring. Death by 1000 cuts.