What I'm trying to communicate is lost. I can try again?
I shared my experience because I thought it might help explain how adults sometimes do just cut ties, for whatever reason, and really all you can do is respect that. It would be wrong to "stalk" them, right? What I'm getting at is, Nancy would not have been considered a child at 21 in the 1970s. I'm not sure how old you are, but it was really different generally than it is now. Even with teenagers who ran away, and whose families DID make a real effort to find them a lot were dismissed. So a 21 year old, it likely would have been like "Hey, she's an adult, she can come and go as she likes." I do think LE probably told them this.
Nancy checked herself out of the halfway house and resigned from her job, and she's in East Bumblewacky, Vermont probably they just thought she was a hippie. A lot of young people were, even if yes as you mentioned, the war was over. You should have met some of the parents of kids I went to school with, and the names of some of my classmates LOL. I'm crunchy around the edges, but oh man....anyway....
When I listened to the interview with the sister I personally found it a bit confusing as to whether the sister of their mother has Nancy go stay in a hospital for her "well-being"m and for how long. It would have been interesting to know more about this, but it was all a bit jumbled, IMO.
And again, if Nancy was 21, and you consider her a child, how old was her younger sister? 20? 19? 18? If the younger sister had Nancy committed to a hospital she was probably 18-20, so legally an adult, but a young adult. I would think that is pretty stressful, wouldn't you? She would have had her own life as well--college or a job, personal life, whatever was going on with the mom and stepfather, a younger brother whose age we do not know, possibly step siblings. Her older brother was married and settled down in another state.
It sounds like the mom and the younger sister tried to be supportive in sending Nancy clothes to Brattleboro. Someone reported Nancy missing. In the 1970s, 1980s, 1990s, what should they have done to find her? And again, we do not know what they DID do, or what sort of family conversations they had.