Answer: D) Dissociative identity disorder
Explanation: Dissociative identity disorder can be simply refered to as a form of mental illness or disorder where the patient maintains two or more distinct personality states. People experiencing this disorder tends to completely dissociate themselves from a traumatic experience by trying to copy and exhibit a different personality entirely. Dissociative identity disorder is usually caused by severe trauma, emotional or sexual abuse.
With Vanna's constant change of personality state, she should be diagnosed with dissociative identity disorder.