First put Irvine in your party and get his strength as high as you possibley can Demi junctions rather well and you can give him a GF like Ifrit to help boost his strength with the +20%/+40% abilites. Next make sure you have either AP ammo or pulse ammo. You can get AP ammo by modifying Chef’s Knifes, and pulse ammo by modifying energy crystals. The only other thing your going to need is either some aura spells, or aura stones.
When you go into battle with Adel have one of your other charecters cast aura on Irvine, or use an aura stone on him. Then just use his limit break to shoot the crap out of her with one of the two ammo types I mentioned above and she should be K.O.’ed in no time.
Now I wanna play FFVIII again…
Edit: And now this topic is closed because its bad title and another thread being started covering the exact same thing with a better title.