Don't get me wrong, I love the character development that Riku got as a result of the events in KH1, but I don't think I would like it if something similar happened to Kairi. For one thing, the issues that led to Riku's fall had been festering for years, as Xehanort's Heartless indicated before battling Sora. He'd been dying to escape and get off the islands, and eventually it got to be too much, so he left his world to be swallowed by darkness all in the name of his big adventure.
Kairi doesn't quite beat to the same drum. While I believe her situation throughout the "Days" period led her to get desperate enough to want to leave the islands, it was all about protecting and helping her friends. She was worried that it was taking them too long to get back, and hated that they had to do all the dirty work for her. So when Axel and Pluto came along, she jumped right into the dark portal without a second thought. Can that be exploited by someone like Maleficent? Absolutely. But I don't necessarily believe that's the route that Square will, or should take.
I don't think that Kairi's flaws rest in any desire to make herself more important for her own sake. Her main problem is that she doesn't have the skills necessary to match her desire to help. I think it would be better if we saw her tagging along with Sora and Riku, only to truly come to understand what Sora meant by being in the way. I see her getting them into worse trouble than they would have been in normally, and learning that there is a time and a place to jump in swinging. Basically, she'd develop into a more reserved person who has to find her niche in the group and how she can best help them, while learning to become a better fighter.
