frontierswoman vs adult female

frontierswoman and adult female both are nouns.

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

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

Other hypernyms of frontierswoman include pioneer, woman.

frontierswoman (noun)	adult female (noun)
a woman who lives on the frontier	an adult female person (as opposed to a man)