Mina's a popular, outspoken African-American girl who’s in Dicey’s grade at school. She works hard to be Dicey’s friend, despite the fact that Dicey is white. As Mina’s popular black friend says, "I don’t know why you’re looking for honky friends" (5.135). Here’s the answer: because Mina sees that Dicey’s a weirdo just like she is, under the surface, at least.
After Mina proves her loyalty by defending Dicey against Mr. Chappelle’s accusations of plagiarism, Dicey grants Mina the honor of walking her to her after school job. As they stroll, Mina says, "That’s what I like about you, Dicey. With everybody else, they want to talk about boys, or clothes, having babies. You know?" (9.128).
Even though Mina talks about subjects that are uncomfortable for Dicey (namely, girly stuff), Dicey lets Mina be her first friend in Crisfield. Mina gently insists that Dicey reach out to her, then waits for Dicey to summon the nerve to do it.