but that the character's only lines of dialogue were basically 'hi, i'm trans'. said to a person they didn't know, in a setting that contains some really nasty, vindictive people.

Like I said in another comment, this is basically how the vast majority of all unimportant NPCs in Baldur's Gate (and most D&D games, honestly) operate. You speak to them, they greet you, you get maybe 1-3 dialogue choices, they give you a few lines that can be anything from talking about the weather to giving you their entire family history, and then you move on and never speak to them again.

In this case, you and her greet each other, and then there's 1 dialogue option that you can choose where you mention her name is rather odd, to which she replies that's because she made it up herself as she was raised as a boy and her old name didn't fit when she became a woman. That's it. It's just a bit of fleshing out for a throwaway character that you'll only meet once. Hell, you don't even have to ask her about her name, you can just say hello to each other and then walk away, it's not being thrown in the player's face or anything.

Re: the setting - sure, there are a lot of nasty things about in the setting. Transphobic things, though? Who knows. Since this is the first trans character we've had in BG, there's no way to know if transphobia is really a thing or if, in a world full of magic and sorcery (including sex-changing clothes and spells where you can polymorph people into various creatures) it's just seen as something pretty tame and unimportant.

The game does have many flaws - most of them related to the technical side of the game. Writing-wise, it's very standard Baldur's Gate. So the fact that 99% of the rage I see directed at it is about "sjw writers" and "pushing agendas" is pretty damning.