valley girl vs young lady

valley girl and young lady both are nouns.

Word	Noun	Adjective	Verb	Adverb
valley girl	Yes	No	No	No
young lady	Yes	No	No	No

As nouns, young lady is a hypernym of valley girl; that is, young lady is a word with a broader meaning than valley girl:

valley girl: a girl who grew up in the tract housing in the San Fernando Valley
young lady: a young female

Other hypernyms of valley girl include fille, girl, miss, missy, young woman.

valley girl (noun)	young lady (noun)
a girl who grew up in the tract housing in the San Fernando Valley	a young female