Nouns that descrice a girl that starts with the letter N?

Nouns are not describing Words; adjectives describe a noun. The Word girl is a noun.

Adjectives to describe a girl that start with N may be nice, naughty, neat, needy, or nonchalant.

If you need a noun, then you are looking for synonyms; some synonyms for the Word girl are nurse, nurse's aide, nightingale (singer), naturalist, nanny, nun, niece, Nancy, Natalie, Natasha, neighbor, native, navigator, Norwegian, Nepalese, Nicaraguan, etc., etc.