Final answer:
The client's statement, 'It still doesn't seem real,' in response to a sexual assault indicates the use of the defense mechanism known as denial (A). This mechanism helps the client avoid the full emotional impact of the traumatic event, and the nurse correctly considers a mental health referral due to the extended use of denial.
Step-by-step explanation:
The defense mechanism being displayed by the client who was sexually assaulted and feels like the assault still doesn't seem real is denial. Denial is an unconscious defense mechanism where a person is faced with a fact that is too uncomfortable to accept and rejects it, insisting that it is not true despite what may be overwhelming evidence.
In this context, the client's expression of the assault not feeling real might reflect a refusal to fully integrate the reality of the traumatic event, a common response to overwhelming emotions associated with trauma. Therefore, the nurse's consideration to request a referral to a mental health professional is in response to the client's extended use of denial.