As I explained, Minsc is just as weak and in need of rescue as Aerie, they're just different sides of the same coin. And yes, she fits a lot of the details of the Damsel in Distress trope. But it's still not sexist, because her condition has nothing to do with her gender, it's a result of experiences that would've broken any man or woman. The picture her writers paint isn't that women are fragile, it's that trauma victims are fragile.
I think even her passivity and lack of sidequest may be an intentional part of her characterization. It's a common thing among PTSD sufferers. A friend of mine has a brother who fought in the war in Bosnia. He's 40, strong as a bull, and far from incompetent at manual labour. But he's spent the last ~20 years living in a tiny house with his aging father, with no other people within an hour of walking. He just watches TV and waits for his father's retirement check so he can drink by the TV for a couple of days and get into fights with his father. He has like three war stories he always tells, and they're all about how he didn't kill an enemy soldier when he could've. Most people just call him lazy, but I can tell there's something more to it. My best guess, based on the apologetic stories he keeps telling, is that he killed someone and just can't get over the guilt.
Now, Aerie's PTSD was caused by a completely different thing, but the common note is being unable to cope with everyday life due to being stuck in the past. The only question is the point of such a character being in the story. I think the problem that the writers were facing is that fantasy worlds in video games are automatically seen as simplistic, so she was needed to establish a somber atmosphere. Her "good" ending not being all that good just makes the world even more real, because in real world there's no happy endings for people like her either.