farm girl vs little girl

farm girl and little girl both are nouns.

Word	Noun	Adjective	Verb	Adverb
farm girl	Yes	No	No	No
little girl	Yes	No	No	No

As nouns, little girl is a hypernym of farm girl; that is, little girl is a word with a broader meaning than farm girl:

Other hypernyms of farm girl include female child, girl.

farm girl (noun)	little girl (noun)
a girl who has grown up on a farm	a youthful female person