“Seven or eight years ago, she started making waves with her chamber-ensemble-cum-girl-band, Victoire, a group with a funky alt-classical vibe that she formed as an outlet for performing her own music. Listening to the band’s post-minimalist drones overlaid with expressive spasms of melody in an electronic haze, playing at the Atlas on H Street in 2011, you might not have guessed that Mazzoli’s work was going to veer into the world of mainstream opera. But on Friday, the Washington National Opera will be presenting the world premiere of her third opera, a 70-minute piece called “Proving Up,” and the opera world counts the company lucky to get it.”