Looking for 1/2 sister born 1966 in PA

My mother gave a daughter up for adoption in 1966. Her birth name was Margaret. My mother's last name was Graham. We think she was adopted into a family somewhere on the Main Line of Pennsylvania. My mother stayed at the Florence Critendon Home in Germantown, PA during the later months of her pregnancy. Any information would be most appreciated. My family would love to know she is OK! She has 2 half sisters (me and my younger sister, Sue) and a wonderful birth mom, who has thought of her EVERY day.