I don’t even trigger her at all. That fight can be fucking cancer at higher difficulties. What I do is make sure I enter the shadow cursed lands from the mountain pass. that puts me near the drider’s group and I just slaughter them and free the pixie. Then I never have to talk to Isobel and that fight never gets triggered. They even made a specific scene for this scenario if you go back to the Last Light after freeing nightsong and never having met Isobel.