I've dabbled in writing and have looked at numerous writer guides to get better. One of the main tips is to show, not tell.
With SH, all they've shown during her romance is a slow burn romance throughout the game. Aside from some light flirting with other companions, she only shows serious interest in the player.
We simply haven't been shown anything different, outside of optional side stuff. People can engage in this side content or even headcanon all they want but the slow burn romance is the only thing that is truly canon if you romance SH. And unless the writing is changed, that's just how it is.
You would expect her to act a little bit different in those sitiations.
How so? The drow twins and Halsin are there specifically to cater to those who want group sex content. Of course they're going to make her into it. She's into whatever you make her into, to please the player. Her and Astarion are both designed for anything and everything, yet OOC when they do it. As I've said before, it's optional side porn quest. Not canon. If it were, it would have been made part of her main quest/romance.
