I've worked with people for almost a year without remembering their name, because I'm awful with names. They were also very quiet and introverted, rarely said much and I suspect that had something to do it.
I recommend starting out by assuming she has knowledge and experiences you don't have access to and learning from it, rather than trying to explain away this new information.
Gaslighting is something that happens over a long period of time, with someone you know well and that you trust. The person you are defending is not going to be questioning their sanity or who they are as a person because of one HN post.
Asking someone to reconsider why they were treated a certain way by other people is not gaslighting. Calling someone a liar is not gaslighting. Countering someone's anecdotal evidence with your own is not gaslighting. Please stop trivializing the term, because it's a serious form of emotional and mental abuse, and you're downplaying its severity by tossing the word around like this.
I'm not blaming anyone, just trying to share another perspective. I personally think it's dangerous to think in black and white. I try to remain a healthy skeptic, and I'm welcome to new perspectives.