Looking for birth parents 9/9/78

Hello my name is Deanna. MY half sister was adopted. Dob is 2/20/1977. Born at lawton indian hospital. Cherokee heritage. Her birth name was Sonya marie wilson.she had an older brother born In 1974.. 3yrs and 3 months apart. My mother was sick and she was adopted at three months old out of the Dallas area.I have been told that people where able to alter birth certificates of adoptees during the the 70's. It was a closed adoption. The lawyer told my mom that the family adopting Sonya was well off. My mom was told that the adoptive mother was a previous pagent contestant or possibly a winner. The adoptive parents possibly already had two biological boys at the time of the adoption took place. Could this be you?thank you Deanna