No you are doing it wrong, forget about getting other cards, when you enter the region while you are at max health just head straight for her, once your there just do a combination of shields and attacks, and youll win, i won against her 2/3 by now so I could watch her scene again but overall just keep moveing between shields and attack, youll whittle her down eventually, I was at 16 and she was similar the second time while before she was 22 and I was 22 and at the last moment I got her down with luck since she tried to heal and I took her down, basically just play the long game.
