The correct answer is D. An appositive phrase to present more information about Fran.
Step-by-step explanation
An appositive phrase is a writing resource that is used to explain a noun mentioned before. In the case of the phrase "Yesterday, Elise finally stood up to Fran, the meanest girl in the whole school" the appositive part is "the meanest girl in the whole school" because it explains the noun Fran by mentioning the main characteristic of her personality. According to the above, the correct answer is D. An appositive phrase to present more information about Fran.