girl vs lady friend

girl and lady friend both are nouns.

Word	Noun	Adjective	Verb	Adverb
girl	Yes	No	No	No
lady friend	Yes	No	No	No

As nouns, girl and lady friend are synonyms defined as:

girl and lady friend: a girl or young woman with whom a man is romantically involved

Other synonyms of girl include girlfriend.

girl (noun)	lady friend (noun)
a young female	a girl or young woman with whom a man is romantically involved
a girl or young woman with whom a man is romantically involved
a youthful female person
a friendly informal reference to a grown woman
a female human offspring