Who is Sarafina from Tender at the Bone: Growing Up at the Table and what is their importance?

When Ruth goes away to college, her roommate is the beautiful, exotic Sarafina. The two girls quickly bond, a connection that is threatened when Sarafina learns from her adopted parents that she is half African American. Sarafina rejects Ruth to hang out with black friends, but the two eventually bond again over a trip to northern Africa.