Signora primarily uses a Cryo delusion to produce attacks and in the storyline as well. We see her using her Cryo abilities against Venti and then later the Traveler during the battle at the Tenshukaku. Although her true element is Pyro, her delusion was given to repress the Pyro aspect of her abilities. Also, no, her Pyro abilities do not originate from a Pyro vision. Instead, the Pyro abilities originate from her own body. After the death of her lover Rostam, Signora used her life's "flame" to purge the world of all entities responsible for his death. Her rage and hatred manifested themselves in the form of Pyro after she used the art of liquid flame to turn herself into a Pyro entity, earning her the title "The Crimson Witch of Flames."