Girl can be used in almost any situation and just refers to  a female of any age,however ,its more common to use the term for females under 30

lady can be used in almost any situation,and is more respectfull .there is a common term called lady like,which implies that  ladies act like females should.they are carrying pleasant and have good manners
1 5 1
Lady is a older then a girl who can decide anything which she want but a girl is a small thing which cant decide her own what she want for her.....
1 5 1