The levels and the party you have are fine, I had nearly the exact same stats when I defeated her recently. If your having trouble with her attacks even with Immunize then there might be a problem with your equipment, I'd recommend buying some defence boosting gear, at least for your front-line and ...

Killing the Royalant with an Ice attack usually results in an Ant's Jaw. It's not a 100% drop, but it greatly increases the percentage.