Are you sure Schala doesn't fit in Robo's graphics? Robo is the largest character and he doesn't have any "halved" animations like Frog and Ayla, so there should be enough place. For her weapon, she could use magic beams or stuff like that (like Edea in FFVIII). Of course, the hardest part even when you've done all her sprites, is to cut them in small squares and paste them over the disorganized Robo slots... but it's not impossible.