Final answer:
The title that best encapsulates the essence of the story about Nia's dilemma is 'C. Nia's Choice,' as it directly addresses the main conflict regarding her decision-making.
Step-by-step explanation:
The title that best fits the focus of the narrative where Nia has to decide between fitting in with the cool kids or abiding by her parents' rules, is C. Nia's Choice. This title encapsulates the central conflict of the story which revolves around Nia's personal decision-making and the consequences it may have on her relationships with both her parents and her new friends. Titles like 'Fitting In' or 'The Forgotten Phone' may touch on elements of the story, but they don't capture the essence of the narrative as well as 'Nia's Choice' which directly reflects the dilemma Nia faces.