ISO Birth Sister born in DC in 1968

I'm looking for my sister that was born in 1968 at Providence Hospital in Washington, DC. I believe my mother named the baby girl Stephanie Marie. I'm not sure what the last name would have been, either Mangum or Nelson. I believe the adoption was done through some kind of catholic group in Maryland. My mom and dad were only 16 and 17 at the time of the birth. They are still together and had 3 more children (1 girl, 2 boys).