Not being told that certain opportunities are open to you because of your gender is sexism. This goes beyond child hood. People assume because of you're gender you will or will not be into certain job prospects and other activities. This is sexism.
I wasn't told it was a possibility either, and I'm male and went to an all male school. Depending on how old you are (I'm mid 30s now so school in the early 90s) and how behind the times your teachers were, I reckon it was pretty common for people not to understand that there was a career to be had in computers. This could be down to plain ignorance of how important they were going to become. I only realised it was an interest after starting and hating an engineering course in 96, because all school ever told me was 'here is a machine you can use to write documents and make pictures'.
Of course if the reason she wasn't told was because of her gender then sure, inherent sexism.
If I hadn't gone into software, I may have ended up in some other engineering discipline. Growing up I saw both boys and girls encouraged to go into engineering, but not into computers. Even as a male, I feel I'm working in software despite the culture I grew up with as a child.
I never see this point come up much but I can tell you that when I was growing up "geek" was a pejorative term and the guys who were into computers were largely social outcasts. I can remember in high school the kinds of guys who sat on IRC chatting with their little "cyber friends" being made fun of. And I don't think they ever got much of a chance to "exclude" girls since my bet is most of them never had much luck getting one to talk to them in the first place. I don't doubt that sexism helps fuel the gender gap we see in tech, but sometimes it seems like people forget that the original demographic in this industry was by and large made up of socially awkward males who pursued their hobby despite being looked down upon and excluded by others, not because of the heaps of encouragement they were receiving.