Chelsea is tall, elegant and beautiful like Rosalie and Heidi. She has red/black eyes.
Chelsea can read the ties of people, like Marcus. but she can also influence those ties. She can make people turn away from others, and also strengthen the bond of one person to another. Aro used this power to keep Marcus loyal to the Volturi after his love, Didyme's, death. Her main purpose in the guard is to separate the guilty from the innocent by breaking their relational ties. When a vampire turns up that Aro is interested in, she strengthens the ties of that vampire to the Volturi, to influence them to serve willingly. However, as stated by Edward Cullen, she cannot as easily influence the emotional ties of people when those ties are stronger than just friends or acquaintances. She could not have changed the way Edward and Bella felt about each other, for example. Her power is also mental as proven when she tries to bind Bella, Edward, Benjamin, Zafrina, and Kate to the Volturi during the conflict in Breaking Dawn, but was unsuccessful due to Bella's shield that blocks mental powers.
Chelsea means 'port of ships' in Greek.
She has a spouse, Afton, who is part of the Volturi guard. He has unknown special powers, but not much is known about his character.