When the "child" is an adult of 31, that's a good time to be friends. The parent-child relationship needs to be a parent-child relationship when the child is still a juvenile; when the child has reached adulthood, a healthy parent child relationship will be that of two adults. If you raised her to not have appropriate boundaries with people in her life, that's a different matter, but should be handled in the way you would handle it with any other adult, whether you gave birth to her or not.