She is not writing about things that affect me or things I have ever encountered.

This is something I wanted to bring up in my first reply but couldn't really find the words for. Later you mention:

she probably sees sexism or discrimination in almost everything she interacts with

So here's the thing. At some point in your life whether or not you are a part of these groups in society it is inevitable you start noticing the big offenses, so to speak. Things that are by and large universally recognized as unacceptable. A person was assaulted. A person was denied treatment. These don't happen to everyone (though are honestly more widespread than most want to believe) and not usually to you or someone you know, so it's easy to detach yourself from the people that are affected and focus more on "the issue" - which is sort of a misnomer and brings us things like "reverse racism" and MRAs. But I digress...

Then something happens. You start noticing these peculiar little behaviors that are difficult for everyone else to see. These usually take the form of slight insults, intentional or not, and they can come from anywhere. One of your friends calls someone a bitch or a pussy in your presence. Being talked over by the guys in the group. Men start taking up more room in buses for some reason. Waiters talk to you last.

And it's these things that people don't notice, because they are learned behaviors that are so ingrained in our society so as to be seen as innocuous if not completely normal. Lest we forget the classic, "I'm not sexist. Some of my best friends are women!" or "I don't see you as a woman, you're just another person." Unsurprisingly, you can replace all forms of "woman" in these examples with "black " or "gay", "sexist" with "racist" or "homophobic", and hopefully you start seeing the pattern. This is when it starts becoming hard to talk about, and you start getting frustrated.

Bringing me to my point: most people don't realize it, but there actually is sexism and discrimination in almost every interaction in our lives, big or small - if you're a woman or another minority, that is. How much of people telling you what happens to you isn't really a problem in spite of these lived experiences until you start getting mad?