The Witch Mates(Alec Volturi) currently on hold

Alec and his twin sister Jane are known as the 'witch twins' of the Volturi clan. they are feared by both human and vampires alike, they are the higher guards along side with Demetri and Felix. But what if there was another high guard but she is only sent in for the hardest jobs the ones that NEED to be done quickly and viciously but they require a certain...... style. something that makes the offenders remember that the Volturi don't give second chances.
Her name is Grace Elizabeta Volturi and she is Alec's mate and Aro's superpower.