Final answer:
The most representative skill associated with the working phase of the helping relationship in this scenario is facilitating the client's expression of emotions.
Step-by-step explanation:
In the helping relationship, the working phase involves actively assisting the client in dealing with their issues. Based on the given scenario, the nurse's statement about feeling frustrated is encouraging the client to express their emotions, which is representative of the skill of facilitating the client's expression of emotions (option C). This skill helps the client acknowledge and process their feelings.
Establishing trust and rapport (option A) is typically part of the initial phase of the helping relationship. Exploring and understanding the client's feelings (option B) is important throughout the relationship, but it is not specific to the working phase. Providing information and problem-solving assistance (option D) may be relevant, but it is not the most representative of the skills associated with the working phase.