The point isn’t about who could have raised the kid better, the point is, who is the kid emotionally bonded to?
By that logic, all adopted children are victims of the Stockholm Syndrome. From the child’s perspective, there is no difference between infant adoption and infant kidnapping, if it was a situation where the kid didn’t know about the circumstances in which she came to live with her birth parents. By definition, the person has to know they were kidnapped in order to suffer the Stockholm Syndrome. In fact, if anything, you have it reversed…taking her away from the only family she had ever known, and giving her back to the bio family would be more likely to cause Stockholm Syndrome than what she has experience with her adoptive family.