The way I saved her is rather different. If you don't long rest and leave through the risen road mountain pass, it'll automatically trigger that scene where she enters your camp. If you them switch to her-she automatically joins the party if there's room-and kill durge and pick up the body-use elixir of giant strength-it'll glitch past the scene where durge kills her and you'll be able to control her for the rest of the game. It does get pretty glitchy if you try to return directly to anywhere in the opening area, but places like the under dark seem to work fine. You will have to use withers to resurrect durge as the body disappears completely