The speaker compares herself to a candle, and the comparison cuts two ways. A candle is small and quiet, but it can start a fire if things go wrong. In the same way, she says she can "cause fire very easily," which suggests she knows she has real force in her, whether that's anger, passion, or the ability to affect people around her.
Then the poem turns. All it takes is "a sigh" to blow that power away. The word "simple" matters here: the thing that defeats her isn't a storm or a fight, just a breath. That makes her seem fragile and a little frustrated, as if her strength depends on how others react to her. The title, "Just a girl," adds to this, since "just" hints that she feels dismissed or underestimated. The mood is quiet and wistful, with a thread of resentment underneath. It's a short poem, but it captures the feeling of being strong and vulnerable at once.