What is the role of one minor character in The Piano Lesson?

In August Wilson's play The Piano Lesson, there are a total of 8 characters: Berniece, Boy Willie, Doaker, Lymon, Maretha, Avery Brown, Winning Boy, and Grace. There is also Sutter's ghost, who is not exactly a character and is never seen onstage, but definitely has an important presence throughout the storyline. 
Maretha, an eleven year old girl, is Berniece's daughter and Boy Willie's niece. The Piano Lesson is centered on ancestry and legacy, and Maretha is a walking, talking representation of the possibility for the future of this family. They could keep the piano that painfully reminds Berniece of all the sacrifices their enslaved ancestors made, or sell it in order to buy the land that Boy Willie believes will be their legacy. There is a lot of arguing over what Maretha should know about her family's past and what would be best for her future, so one could say that she functions as a representation of the conflict between Berniece and Boy Willie.