As a frontwoman, Nina Diaz has the not-so-common ability to slide from sweet and endearing to snarling and intense in an instant — and both sides seem equally true to her musical identity. That kind of dynamism is just one reason why San Antonio’s Girl in a Coma is so compelling. There’s also the cohesion between Diaz and her sister/drummer Phanie Diaz and bassist/friend Jenn Alva — and the songs, of course, which contain the brash energy of punk rock. The members are also huge Morrissey fans (the band is named after a Smiths song) — a phenomenon in the Chicano community that they discussed on the radio program Latino USA two years ago (Nina cited his passion and lyrics as being a contributing factor). After getting signed to Joan Jett’s Blackheart Records label early on, Girl in a Coma went on to tour with Morrissey himself, as well as Social Distortion, Frank Black, and others. These days, the band has its own headlining draw — see why at the Rickshaw Stop (155 Fell St., San Francisco), with Hunter Valentine and Krissy Krissy opening.