Heroine Complex is urban fantasy. It could also be considered superhero fiction. I bought my copy used.
Review:
A few years ago, demons tried to invade Earth via interdimensional portals. They failed, and for some reason several humans ended up with superpowers as a result. Aveda Jupiter (real name: Annie Chang) is one of them, and she's now San Francisco's most beloved and hardest working superhero, battling the much weaker demons that occasionally turn up. Evie Tanaka is her childhood friend and personal assistant. She's used to dealing with Aveda's tantrums and is, in fact, an expert at making sure Aveda's public persona remains perfect. Evie always keeps her emotions in control, even when work is stressful or Bea (her younger sister, who she's been raising since their parents died) acts particularly rebellious. Because she knows if she slips up, she might accidentally kill someone.
Most of the superpowers people got after the demons came were relatively weak. Aveda, for example, got telekinesis, but she can only just barely move things. Evie's power, on the other hand, is much more dramatic and terrifying: she can light things on fire.
When Aveda injures herself, she convinces a reluctant Evie to pose as her for an event, during which Evie accidentally reveals her superpower. Now Evie's stuck pretending to be Aveda for a while longer, even though she'd much rather fade into the background and let Aveda have the spotlight.