The last time Texas guitar virtuoso Carolyn Wonderland played at Jazz Fest in 2018 was an especially memorable one: It was her debut with British blues legend John Mayall, and she was so new to the band that she hadn’t met them all, much less rehearsed. “It was beautiful and frightening,” she recalls. “I had just been sent about 80 songs to learn, and I just hacked them in terms of keys, what f...