Unconditional positive regard offered in therapy means that whatever Sarah says and does, it will not negatively affect the therapeutic approach used with Sarah. Unconditional positive regard will help her to build confidence in her achievements. 

Acceptance and acknowledgement of Sarah as a person in her own right will help her develop a healthy self-esteem and confidence.

What could Poppy do to prevent a similar incident occurring in the future?

Poppy could have asked the named nurse or checked nursing records of the gentleman so that she knew his reason for admission prior to entering the room.

How would using PERFORM have helped Poppy in this situation?

Although Poppy managed the situation correctly she was intuitively responding to it. Her focus was the task and she was anxious about her performance in relation to this and so did not focus on the patient. If she had been using PERFORM she would have prepared herself before entering the room for meeting with him and his relatives by finding out his name and preparing herself by thinking  through all the aspects of PERFORM (her eye contact  facial expression and managing herself etc).