"És uma menina."
This is Portuguese of Portugal, not Brazil. Você conjugations are identical to those of ele and ela. You differentiate from them by using the pronoun, i.e. "Você é uma menina" (You are a girl) versus "Ela é uma menina" (She is a girl).
But it's not wrong in Brazillian Portuguese, the 2nd person still exists, and it's widely used in the south and northeast regions.