She's not actually a dragon...
Just as an infant is more susceptible to germs and illness, so are they susceptible to magic. In fact most don’t like using magic on babies because it sometimes has unpredictable effects. So is what happened to Dracy. Her mother, still pregnant but nearly due, was kidnapped and used as blackmail to get her father to steal a magical artifact from the king’s treasury (he was a guard of the treasury after all). The stress of the kidnapping causing Dracy’s mother to go into labor and have the child. When she was mere hours old, Dracy’s father arrived with the artifact. The man who had kidnapped them, a man named Morcun, threw Dracy to her father, who managed to catch her, but slit her mother’s throat. Her father used his magic to escape with her and the artifact. With the help of a dragon, he used the artifact to transport he and Dracy to another world. The artifact was dragon-based magic, so when they came over to the other side, the infant was changed. Dragon scales covered her back, and she had wings she could shrink and retract into her back.
Her father was found by Peter, and helped to find a means of living in this strange world, raising his daughter, hiding her dragon-like tendencies. But one day he goes missing, and Dracy is at a loss, until she is attacked by a strange man, only to be rescued by Peter, who sends her back to the world she was born to find her father and partake in helping save the world.