Yeah, I agree with Sliv. Even had things gone down differently in the aftermath of Ion's death (ie Anise properly explains herself, the duel to the death is avoided, the status quo is basically returned to normal), Arietta's mad-on for Anise would have continued; Arietta wouldn't be Arietta if she was in any way a reasonable or rational person capable of changing her mind, after all. The only way I could imagine Arietta joining the group's party would be if Ion for some reason asked her to.