kinswoman vs adult female

kinswoman and adult female both are nouns.

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

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

Other hypernyms of kinswoman include relation, relative, woman.

kinswoman (noun)	adult female (noun)
a female relative	an adult female person (as opposed to a man)