That's correct! You'll either need to cast a defense buff on yourself or an attack debuff on her before the attack hits. Better equipment and leveling up might help as well if you can! Having a healing spell equipped is a good idea as well if you don't have one already. Also, swapping characters does heal you a little bit!
At 2x difficulty though, she essentially deals double damage, so it's gonna be tough either way ^^
I've updated the game by the way, you should be able to just redownload it and your save should work as is! You won't be able to get back the item you lost, but at least consumables will be saved normally from now on. Sorry about that!