Fiammetta, from the Italian word for flame, has both femininity and fire. Fiammetta could make a good alternative to more conventional Italian girls' names like Giovanna.
Fiammetta has some romantic, if not fiery, references. It was the pseudonym of Boccaccio's beloved in the Decameron and other works (the subject of a famous Pre-Raphaelit painting by Dante Gabriel Rossetti); and another Fiammetta was a famous courtesan and lover of Cesar Borgia. Currently there is a hot Italian cover girl named Fiammetta Cicogna.