Yet she doesn't follow through with either of those propositions for casual sex with you. Are there examples of her with other companions? Lae'zel openly has casual sex at the grove party, it makes no sense SH doesn't do it as well if she's sooo into it.
I only consider her main story quest and the choices you specifically make in it, and it alone, to be canon, for her. You can't ignore her main story. You can kill her and end her story, but that still counts. You cheating on her with Mizora is a completely optional choice, and you are not forced to do it. Therefore, it is not canon.
No one else makes a move on her except Wyll, who does it AFTER failing to impress Lae'Zel so Shadowheart writes him off. I was just discussing in those same posts how she pretty consistently lacks personal initiative. The only time she displays any at all is once you've already made her quite happy and more of an open book in your relationship, at which point she shows more confidence in asserting what she wants for herself. And again it runs through your choices, she only takes initiative for something you first show a shared interest with her in (which is yet another reason the act 3 Halsin stuff has to be revamped). It makes the ACTUAL inconsistency with Karlach stand out all the more because SHE'S the one who seems totally accepting of poly with Shadowheart, only to find out the timing of game events makes it impossible to achieve because Larian didn't fully develop the concept (or Karlach's own personal quest which might have also changed things in Act 3).
And I'm just not going to address anything about canon further with you, our views are entirely too incompatible for any discussion about that between us to be even remotely enjoyable or fruitful.