Let her summon her dragon, wall of d her, flame wingman for 2400 effect damage. I got lucky to do this on first try. Take note that it's a specific lvl akiza, I think it was lvl 30. Maybe u just doing the wrong difficulty
Just use the cloudian nimbusman along with the continuous cloud counter spell, you can easily get him above 10,000 against most decks and just one shot the guy. Getting over 9999 damage in one hit awards 3000 Duel score!