Answer:
Option D, dissociative identity disorder.
Explanation:
Dissociation occurs when a person's mind is unable to establish connections between his/her thoughts, emotions, memories, feelings, or even a sense of identity.
Dissociative identity disorder occurs when the person displays 2 or more personality states, each one with its age, sex or race.
Alexia suffers from this disorder, and "Clara" maybe her second personality, who is totally disconnected from Alexia's reality, and that is why she doesn't even remember who Alexia is.