The Fire Rose by Mercedes Lackey

In Edwardian London, an orphaned young woman with a rare gift rises from poverty to fame as a singer, only to discover that her growing power and notoriety have drawn the attention of a dark supernatural predator preying on women. Pulled into a hidden world of elemental magic and rival practitioners, she must unravel dangerous secrets about her past, learn to wield her own magic, and rely on unexpected allies to confront a murderous force that threatens the city and the people she loves.