Ok, I realize a big mistake I had in the game. I thought def reduced magic damage (like how atk boosts both phys and mag), however it seems it doesn't really affect it at all. I grinded 3M for that gold plate thinking it would help me survive her attacks.

Is resilience used at all? I don't think I've seen a book explain it (though I did see a book talk about magic defense, with different wording.)