There are hundreds of boys like this as well. Geniuses get born everywhere, in different bodies, places, social strata etc. The fact that many of them get lesser chances to contribute to the world is an outrageous abuse of the most precious resource that the humanity has, regardless of why it happens.
Possibly men are more likely to hire men, which could cause problems with growth in women's share of the market.
Of course there are also problems like having fewer role models when there are fewer in the industry, not having government and schools enabling women via scholarships, funding, etc. as much as they could, or possibly it's genuine lack of interest, but I don't think that's the case.
Why do you consider a role model in a field of endeavour unrelated to one's sex should be the same sex as oneself? Isn't that just the sort of sexism that you're attempting to avoid??
It seems either women are so different that they need female-centric approaches to programming and aspects, including their role models, must be tailored specifically for them. In which case, that's surely the reason there aren't so many women in tech - that it just doesn't follow the female-centric mores. Or, women and men are alike (ie fit within the same spectrum of abilities, insight and such) when it comes to programming and we should just get on with it and stop pretending people need specific help because of their sex?
The youngest sister may even grow up in a world where she doesn't have the same barriers as most women today.
Could this be a sign of positive change?