Marin in the book is Louie's cousin who stays with his family for the simple reason that hers are in Puerto Rico so it would make sense to stay with family than to go elsewhere.
She helps alot with house chores and babysitting.
She hopes to be in Chicago in the following year so she can find a job and so she finds a rich man who will marry and take care of her even though she also wants to marry her boyfriend in Puerto Rico as well.
