With 2x Vista, Princess Turtle is easy.
Vista/Vista
Diable Jambe Sanji
Helmeppo
Those are all you really need, unless you hit the secret stage. Bring more INT units for the HP increase, I guess.
Strategy:
Stage 1:
Stall as much as you can. With your HP, it shouldn't be a problem. All of your Special should be available by the time you finish.
Stage 2:
Use Vista to win.
Stage 3:
Use other Vista to win.
Stage 4:
Use Diable Jambe Sanji to instantly clear.
Stage 5:
Use Helmeppo and laugh as the turtles fly away in defeat.
Congratulations!
Edit: I just got the Secret Stage. This throws a wrench into my plans...
Never mind. I cleared it. I had Poison Crocodile, Diable Jambe Sanji, and Basil ready to go. I used Basil, Crocodile, and then Sanji. She died before she could attack, and I still had Helmeppo for the final stage.