So the plot thickens...
Didn't want to go through a whole thing to make her survive, so I tried a bunch of stuff, hold her, prone her and whatnot, but sadly whenever she's back on her feet she goes for it, and whenever she's sightable, she gets aggro and get killed.
So yeah, that was that.
But (and I think more and more there are some bugs there...), I get her cadaver whenever I get to a new map (went to the mountain pass, and the next map and each time I get greeted by a dead Lae'zel...
Way to put my nose in it...