The idea that the harassment wouldn't happen if she were old and ugly doesn't make it not about sexism -- anymore than a guy who only patronizes a certain kind of woman (the kind he is attracted to) is not sexist because he doesn't patronize all women equally.
There is a sense which (I think) you're going for where this could be thought of as people latching onto things that are "out of the norm", rather than specifically sexism -- but that seems tautological to me. All -isms (that I can think of) are based on pre-judging based on things that are non-normative: sex, race, age, orientation -- you name it.
What is the norm that she's violating? Well, it seems (to me) to be existing as a (technical) woman in the workplace and all of the attributes that come along with that -- like a human that speaks in a higher register, or wears dresses or doesn't wear t-shirts as regularly.
This is, again, not uncommon and therefore the most likely explanation for all of the things she's encountered taken in totality. "Culture fit", which you refer to, is about prejudice -- and each time the type of prejudice may differ (between racism, sexism, & agism, let's say[1]) but it's still prejudice, not some magical other thing.
[1] suit-ism, let's not forget suit-ism. :-)[2]
[2] Sharp dressed -ism?