I saw someone on Youtube saving her, I think by finding a very difficult (or maybe hacked) way round behind the rock fall, and killing Nere before freeing him. And/or by clicking the Start Combat button in dialogue with Nere after saving him (move the mouse to the bottom left to show the buttons, I don't know how to do it on consoles). But as 1Sascha says, nobody notices what you did, and Meerna doesn't really have any lines either.
