ring girl vs young lady

ring girl and young lady both are nouns.

Word	Noun	Adjective	Verb	Adverb
ring girl	Yes	No	No	No
young lady	Yes	No	No	No

As nouns, young lady is a hypernym of ring girl; that is, young lady is a word with a broader meaning than ring girl:

ring girl: a young woman who holds up cards indicating the number of the next round at prize fights
young lady: a young female

Other hypernyms of ring girl include fille, girl, miss, missy, young woman.

ring girl (noun)	young lady (noun)
a young woman who holds up cards indicating the number of the next round at prize fights	a young female