bride-to-be vs adult female

bride-to-be and adult female both are nouns.

Word	Noun	Adjective	Verb	Adverb
bride-to-be	Yes	No	No	No
adult female	Yes	No	No	No

As nouns, adult female is a hypernym of bride-to-be; that is, adult female is a word with a broader meaning than bride-to-be:

Other hypernyms of bride-to-be include betrothed, woman.

bride-to-be (noun)	adult female (noun)
a woman who is engaged to be married	an adult female person (as opposed to a man)