Maggie Rogers performs at The Observatory OC in Santa Ana on Oct. 18, 2018. Photos: Matthew Eaton. SANTA ANA — As Maggie Rogers took the stage at the Observatory in Orange County, “Dancing Queen” blared in the background, a fitting song for the entrance of Maryland’s dancing queen. Maggie…

Nineteen-year-old Grace Shaw couldn’t believe it: Playing her first non-industry show in L.A. in early April, she spotted superstar producer and collaborator Mark Ronson staring at her from the crowd. Shaw, the real name of Australian singer-songwriter Mallrat, made a bold assertion on Twitter the previous week: Ronson and…