working girl vs adult female

working girl and adult female both are nouns.

Word	Noun	Adjective	Verb	Adverb
working girl	Yes	No	No	No
adult female	Yes	No	No	No

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

Other hypernyms of working girl include woman.

working girl (noun)	adult female (noun)
a young woman who is employed	an adult female person (as opposed to a man)
a woman who engages in sexual intercourse for money