In Lae'zel's terms, think of it in the more mercenary sense - it isn't about *you* at all. From her perspective I view it as more a case of:
"Well, I'm here now and I'm travelling with this lot, and damnit, I'm stressed and in a mood to celebrate and I want some [insert anatomical preference here]. I'm sure as hell not waiting until I find a creche where my superiors will be the ones holding the reins... Who in this lot of slave-fodder material-plane mud-dwelling savages can I use to suit my needs? That one? That one. You, yes you, physically capable flesh being, service me."
Yes. Lae'zel seems the least interested in similarity, or your PCs person, when choosing sexual partners, and she's therefore most unaffected by the approval stats. She's also more appealing within the approval system, since she's the only passable domineering type of companion(Astarion being too much of a sniveling murder-rapey toff, Minthara the-token-domme being a needy slave to the flayer cult etc.) in the game as it is, so it's not like toadying up to her is an unpleasant chore from a d/s kink perspective.
She also seems to enjoy heaping verbal abuse at others, which may give more variety in the dialog options and sort of hints at the possibility that you can have an somewhat antagonistic relationship with her and still romance her. There doesn't seem to be that many dialog options to trade jabs with her at the moment, though, I've seen very few campsite interactions with her. Oddly, she's a bit traditional/poetic/awkward in propositioning to you, as if she has to prop you up in order to somehow justify to her noble self the desire to fuck a lowly servant with a hideously uneconomical nose. And while the 'sex party' plays out like "choose the romantic relationship" -'approval scenario', it sort of works for her, as the romantic relationship with her seems to revolve largely around (enjoyable) masochistic self-denial, since she's got a rather infla.. high confidence in her abilities as a lover/bruiser, and even states that her partner's pleasure should be derived from her pleasure.
There's also little reason to think that she'll betray us for the flayer cult (unless you've been fattening the tadpole so much with your gray matter, that she's lost her wits as well), so there's a chance you can romance her without high approval. Though there will surely be other parties that will try to set the companions at each others throats, so it's possible you'll have to kiss her ass, not just for the sake of it, but because of the approval stats.
But all other current companions seem to be hemmed in by a approval system, that doesn't particularly appeal to me.