Moira Walley-Beckett: “They [the young dancers in the cast] called me Mama Moira. It was a huge priority for me. Because I’ve been there, and I know what it’s like, and I know that they’re all secretly imploding. For most of them, it was the first time they’d been under these kinds of pressures. … It was really important to me to try to keep them safe in every way that I could.”