I'm on my 3rd playthrough, this time as a Redemption Durge. I'm at the end of Act 2, went through the Gauntlet, letting Shadowheart take all the blood sacrifices (to boost her mediocre approval). Went into the shadowfell, defeated Balthazar, and right after the fight Shadowheart goes into camp (ungrouped, but still in the party). If i talk to Aylin, she magically is back in shadowfell to make the talk, i let her take all the dialogue decisions by herself, knowing she values her independence. When Aylin flies away, Shart prompts the "we should get the hell out of here ASAP" talk, and the cutscene is done, she's back in the camp. When i leave shadowfell and go back into camp she suddenly approaches me, saying, and i quote: "I had a choice to make, in the heart of lady shar's domain. But you denied me that chance. Now my future is gone - nothing but windblown ahses and wasted potential". After that she leaves the party no matter what i say.
I reloaded the pre fight save, defeated balthazar again, and when she went into the camp after the "we have to bail from here ASAP" talk i jumped to her in the camp and returned as her to the shadowfell (with the "leave camp" option), which prompted the monologue again, after which she again left. I finally reloaded and let balthazar take Aylin with him to Kethric - she stayed in the party without problem and without ungrouping. I haven't returned to camp with her after that, just quit the game. I'm pretty sure it's a bug, although i haven't seen anyone talk about this, dunno if this is a singular case (which would be very unlucky). Has anyone else encountered it?
