Signora's second form is fully known as the Crimson Witch of Embers.
However, to unleash this second form, she needed to encase herself within a Crimson Lotus Ice Cocoon, shaking off the suppression of the Cryo Delusion on the raging flames within her body.
Therefore, the moment Guchen observed Signora's condition, he knew she was going straight into her second form.
Chapter 110