The whole drow scene and the banter between her and Halsin AFTER you had sex with her (giving the context, that's the most disgusting banter in the game, IMO) was made to accommodate Halsin's poly relationship. And at the same time, destroying her character and development. She's probably the slowest romance in the game and suddenly wants participate in orgies and openly flirting next to the person she says to love so much. It's ridiculous.
This, slowest romance, will break with Tav at any hint of infidelity in act 2, and suddenly she is into orgies, don't buy it, it's just there to accommodate Halsin.
Or you can headcanon it, that she agrees to orgies because she is afraid of losing Tav (after losing everything else in her life), first person who showed her kindness in who knows how long.
But there is still issue of her flirting with Halsin, they should remove that if Tav rejected Halsin.
