This would be hypothetical at best because it's never implied to be the case plus she clearly states she wants you alone regardless. But then you have to remember that the Halsin proposal happens before her final romance scene and suddenly this argument is void.
That said, some minor rewriting and making Karlach an option for open relationship would be the obvious first step to fixing this inconsistent stuff in a direction where she would work as poly, though I'd argue sharing someone you haven't bedded yet is.. odd nonetheless. And then her devotion in act 3 comes out of left field instead.
I think minor rewriting in her conversation about Halsin proposal would do better honestly. To make her maybe less enthusiastic about it? And again just removing Halsin/SH banter or locking it behind double romance only(Alternatively they could rewrite it of course) and tweaking Drow convo(Remove disapproval at least, rewrite scene itself to include options to avoid certain writer's fetish. Or just remove halsin self-insert if not romanced completely) would do amazing already.
She is good as she is, just Halsin stuff needs to be fixed as he is the catalyst for all this.
