In Chapter 3, make sure Ike talks to the Pegasus Knight at the top left of the screen before she gets killed. Do not worry too much; she dodges a lot. She will mumble something about repaying a debt and flies off. If you do this, later in Chapter 9 she will return about two to four turns into the mission. Have Ike talk to her and she will join your team. She is not the greatest, but with a bit of work turns into a very reliable unit. Plus, she flies.