baby mama vs adult female

baby mama and adult female both are nouns.

Word	Noun	Adjective	Verb	Adverb
baby mama	Yes	No	No	No
adult female	Yes	No	No	No

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

Other hypernyms of baby mama include female parent, mother, woman.

baby mama (noun)	adult female (noun)
the mother of at least one of your children	an adult female person (as opposed to a man)