I too have this bug! The moment you agree to go with her the quest fails. Checking it in the Botched section just informs you, "You were unable to help Ellie." Super useful that.
I've tried delaying the quest, going back to an earlier save, or initiating the quest in different locations. It always gives me The Low Crusade quest and always insta-fails it.
Which is awful. Do I ignore her quest for now, or am I just getting further away from some point I'll never be able to go back to in order to fix it?? What if I'm careful not to trigger it, will I be able to start it at some point later? Please, if anyone figures out a workaround, post it here so we can continue with the game. This bug needs to be fixed.
