I need to know more about SH personally to give an informed opinion but my surface-level knowledge of her (never romanced her) is that she's also a SA survivor so I would agree she's not a great option either.

Here's the thing though: if Halsin was truly poly, and SH had given clear indications that that kind of relationship was okay with her, she wouldn't be a terrible option.
But since we get a sex-pest from Halsin and not a true poly relationship, it would likely just be more sexual trauma for her to sort through. This is just my opinion though.

I good alternative would be Wyll, Lae'zel, or Karlach if she gave informed consent.
All 3 characters have the gumption to say no when they're not comfortable with it and, aside from Wyll, they've all expressed that Halsin was handsome and interesting.
SH expresses interest in Halsin but it feels forced and Astarion outright dislikes him, calls him annoying, and makes fun of his nature bullshit all the time. They both just suck as options...

#JusticeForAstarion