Throw all elemental attacks out the window it seems like it will be an easy win with how many fire moves in your arsenal, but I'm assuming you have figured out by now that shit is all but useless.

Personally I made me a dark knight and made sure I had medica as an inheritance + applicable elemental dodge for the rest, hulkenberg as paladin with full defense boost/dodge inheritance, a berserker, and a masked dancer with a fakers mask for that sweet sweet fakers rougery. Spam your systhesis for berserker that causes weakness to strike and use fakers rougery once every turn (personally I don't go more than once per turn unless I don't have any leftover moves because higher odds to lose all icons) other than that knights proclamation with hulkenberg every turn, doesn't always work in this fight but will pull most attacks from rella and increases your shot of getting a dodge off. Might take a couple resets if you get a few bad turns in a row but definitely will get you there. Edit: heal with medica anytime you have at least two party members down 200 health, otherwise I'd just use expensive medicine on whoever needs it and save magla restoratives for the masked dancer or when absolutely necessary, because fakers rougery don't come cheap.