No, I don't find her ditzy. She has her moments (calling a robot Robo, how original, *blech*), but she appears to me as being kind and compassionate more than being actually airheaded. She's also the heart of the team, along with Crono. She's the one who suggested they go and try to stop Lavos when you find out the truth in 2030AD, and that's something that requires guts.