question about afther an adoption has been done.

I was told that I could find some info out here.I hope I can get some help. My husband had an ex girlfriend over 13 years ago to sign over his right of a child that he was not sure was his.He signed her over and the womans husband adopted her.This chidl knew nothin aobut us she was 3 years old when this was done.We have chidren of our own.The womans husband has now died and she told this child that her father is alive and has his own family.She has also told this child lies about us.This child has said mean things to my childrens friends. What can be done when this happens does anyone know?