If you think back, you can probably remember a time when an adult took an interest in your life and encouraged you to pursue a dream or talent you had. There's just something about being a teenager and getting affirmation from an older, more experienced person who isn't your mom or dad that feels oh so good. For Billie Jo, this person is Arley Wanderdale, Cimarron county's own star piano player and local talent manager.
Arley meets Billie Jo giving music lessons at her school, and understandably, he's pretty blown away by her talent. He even invites her, a fourteen year old, to perform with his band, the Black Mesa Boys, at some professional gigs and go on tour. Billie Jo kind of takes this for granted, but think about for a moment: If Arley teaches music lessons, he must work with a lot of kids—and because he only picks Billie Jo and Mad Dog for his ventures, he must have some high standards. Therefore, he's pretty discerning about talent, and recognizes it when he sees it.
Ultimately, Arley's a businessman and his primary objective is to make money and promote his band. That doesn't mean, though, that he doesn't have feelings for Billie Jo that go beyond her talent. When people shy away from her injury after the accident, Arley is the first person to encourage her to get back on her feet (or rather, her piano bench) and get back to work (49.3). He cares so much about her that he even invites her to play some shows, which could have been a mistake since he has a lot to gain or lose from his lineup.
In the long run, Arley's probably the biggest reason why Billie Jo is sitting at the piano in the book's final scene playing for Daddy and Louise. He has faith in her talent at the beginning, but even when it would have been easy and more profitable to throw in the towel, he continues to be her champion. Goodness knows Billie Jo could use one.