salesgirl vs adult female

salesgirl and adult female both are nouns.

Word	Noun	Adjective	Verb	Adverb
salesgirl	Yes	No	No	No
adult female	Yes	No	No	No

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

Other hypernyms of salesgirl include sales rep, sales representative, salesperson, woman.

salesgirl (noun)	adult female (noun)
a woman salesperson	an adult female person (as opposed to a man)