Well, Peej doesn't make even a little teeny tiny bit of sense whatsoever - not only does she not really have the skills, she doesn't have the least bit of interest. She's smart enough to know what leadership entails and she values her freedom way too much to give it up like that, especially not when there are other people around who she knows are way better at the job than she could ever be.
Dinah, on the other hand, does have both the skills and the willingness, if required. She just doesn't have the temperament - it's not good for her, and her friends are assholes for even asking it of her and there's no way she could do it long-term without losing who she is.
Cassie should be a perfect pick, but after years of Johns and McKeever she comes across as the worst of the three. :/