Gibson girl vs young woman

Gibson girl and young woman both are nouns.

Word	Noun	Adjective	Verb	Adverb
Gibson girl	Yes	No	No	No
young woman	Yes	No	No	No

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

Gibson girl: the idealized American girl of the 1890s as pictured by C. D. Gibson
young woman: a young female

Other hypernyms of Gibson girl include fille, girl, miss, missy, young lady.

Gibson girl (noun)	young woman (noun)
the idealized American girl of the 1890s as pictured by C. D. Gibson	a young female