foster sister vs female person

foster sister and female person both are nouns.

Word	Noun	Adjective	Verb	Adverb
foster sister	Yes	No	No	No
female person	Yes	No	No	No

As nouns, female person is a hypernym of foster sister; that is, female person is a word with a broader meaning than foster sister:

foster sister: your foster sister is a female who is not a daughter of your parents but who is raised by your parents
female person: a person who belongs to the sex that can have babies

Other hypernyms of foster sister include female.

foster sister (noun)	female person (noun)
your foster sister is a female who is not a daughter of your parents but who is raised by your parents	a person who belongs to the sex that can have babies