Who is Apple from Tehanu: The Last Book of Earthsea and what is their importance?

Apple is Tenar's daughter. She is described as a bright, kind, and caring girl. Apple is married to a merchant and lives in the coastal town a few miles from Tenar's farm, Oak Springs. When Tenar gets back from the Overfell, Apple meets her and takes her home, after which, they spend several days together.