lady friend vs adult female

lady friend and adult female both are nouns.

Word	Noun	Adjective	Verb	Adverb
lady friend	Yes	No	No	No
adult female	Yes	No	No	No

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

Other hypernyms of lady friend include lover, woman.

lady friend (noun)	adult female (noun)
a girl or young woman with whom a man is romantically involved	an adult female person (as opposed to a man)