I'm not sure it matters too much about her being American, she was taken from one country to another by people who had no legal
rights to her.
As I said, she lived with a family, but did they formally adopt her? Or did she just live with a family?
Harry never signed his parental rights away, so he still has a say, and yeah that can get very messy.
gotta brush up on the subject. But I'm not too sure if her nationality is even listed as American.
If her parents were both American, that is what she is, now perhaps at a later date she can claim duel citizenship because she was born in another country. However she is still an American by birth.
Whether the Carpenters had legal custody or not to little Maggie, apparently they willingly signed her over to her biological father. There was no court fight of any kind, if the Carpenters felt she was in danger by living with her father they would have raised the issue, then the law would have stepped in. The Carpenters fostered her which is different from legal adoption. In most cases the state encourages that children be reunited with their biological parents or parent. While we know all the dangerous stuff Harry has been in the middle of, most of that is hidden from the vanilla law. In short they'd wouldn't find any evidence that Maggie would be put in danger by living with her father.
Actually by that standard a lot of kids could be taken away from good parents because the occupation of the parent might make the kids a target, that doesn't happen. I am talking politicians,
military, police, entertainment, and in some cases medical, all are occupations where the deranged or power hungry might consider their kids fair game, but these kids are not removed from their parents.