Trying to Help a friend locate her Birthmom

Hello , I have friend that was born in Dallas County at Parkland Hospital in 1977. We know her date of birth of course but that is all the information that we really know. We know that they mother was 13 at the time of birth. She was placed with a attorney and that attorney has now passed away . How would we go about searching to locate her birthmother? We do not know her name and we know the birthmother gave her a blanket and card and thats all we know? Any advice on where to start??