horsewoman vs adult female

horsewoman and adult female both are nouns.

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

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

Other hypernyms of horsewoman include equestrian, horseback rider, woman.

horsewoman (noun)	adult female (noun)
a woman horseman	an adult female person (as opposed to a man)