My ideas are kinda basic right now, but here's what I've got:
While Kimitar's out looking for Notai, she meets someone else (either a male lion, or someone that leads her to one somehow) and, for a while, she keeps trying to find her sister.
In the backstory, Notai has managed to find her way home, and the other lions in the pride are worried that Kimitar has died, they look around for her, but give up, assuming the worst.
Later, she comes back to see if Notai made it home and try and convince her to come leave with her.
Of course, conflicts will ensue, and I'm open to additional ideas for the plot.
Characters that will be necessary will of course be the two sisters, Kiara and Kovu, and some of the others should be involved, too.