party girl vs girl

party girl and girl both are nouns.

Word	Noun	Adjective	Verb	Adverb
party girl	Yes	No	No	No
girl	Yes	No	No	No

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

party girl: an attractive young woman hired to attend parties and entertain men
girl: a young female

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

party girl (noun)	girl (noun)
an attractive young woman hired to attend parties and entertain men	a young female
	a girl or young woman with whom a man is romantically involved
	a youthful female person
	a friendly informal reference to a grown woman
	a female human offspring