Have Quistis in your party, and have her cast Mighty Guard. At the same time, have another cast Meltdown on Adel, and have another draw/cast Regen on Rinoa. If Mighty Guard didn't cast Haste on the party then do it manually. Then, just attack Adel with normal attacks. You can have Irvine in the party and use his limit breaks that target only one enemy. You can use Zell's limit break and just not use a finishing move. I would suggest not using Renzokuken because of the possibility of some of Squall's finishing moves. And also, pray that if Gilgamesh comes that he uses Excalipoor.

I would imagine that you are loosing to Adel because of speed, and she's pretty fast. Make sure also that you junction as many characters as you can with a GF that has Spd-J. This will help a lot.