She is the only one that can be turned. Other "can" be, but only if you're the one playing as them which makes it no different than turning your Tav into the squid, except there are some special dialogues like Mystra being able to bail out Gale. Karlach is the third option if you don't want to sacrifice MC or Orpheus
Gotcha, thanks! It's sort of weird in a way that... I can see some other characters having their reasons to volunteer besides the "I'm dying anyway" that Karlach has going? Like, I do think Lae'zel would sacrifice herself in Orpheus's place if asked, for the Prince of the Comet and what not. Then there's also Wyll, one of who's major character flaws is never putting himself first, for the good of the people. (Not that I want anyone to turn, but y'know, theoretically).
I know that Gale can offer to blow up in that scene, which is different, but character-situation-appropriate.
For me it's just the most obvious and painfully generic example of cowardly writer's way out to "raise the stakes". You know, when author wants to have a big death on screen but doesn't have guts to actually kill off some major character so either creates such character or gives one of the existing ones terminal illness or other condition that will inevetably kill the character (for example Thane and Mordin is Mass Effect, Itachi in Naruto, Whitebeard and Roger in One Piece and likely Butcher in The Boys). That's why I think Karlach's engine was never supposed to be fixable, especially knowing that she wasn't supposed to be Origin character, that way OG cast would remain intact, while someone could heroically sacrifice themselves anyway
