Dragon Master by Allyson James

Carol Juan doesn't really believe that her grandmother's friends are dragons, though she'll admit that Caleb and Malcolm are unusual. But when a Fire Dragon, a very rare creature who can not only take human form but turn himself into pure flame, seeks her out, she has to put her disbelief behind her. The arrogant and wild Seth teaches Carol not only about fire dragons, but about her own latent mage powers that pulled him instinctively to her. The secret of the Fire Dragon might help Carol win the day or be the means to her destruction.