A plot could involve Miley's ankle hurting right before she's supposed to go on a secret mission as Hannah Montana. She has to figure out how to complete the mission with her injury. She might use her wits and the help of her sidekicks to come up with a plan that doesn't require too much physical exertion on her part. For example, she could use her charm and singing to distract the bad guys while her friends do the more physically demanding parts of the mission.
One possible plot could be that Miley has an important concert coming up but her hurting ankle threatens to ruin it. Her friends could rally around her, trying to find a solution like getting a special doctor or some magical remedy. Maybe her ankle got hurt during a rehearsal for a new and exciting dance routine she was planning for the concert.