It might have seemed over-the-top at the time. Look at how GF is being criticized about it by some, meanwhile her daughter has most likely been murdered.
We had a bad separation situation in my family - similar to Jennifer, she had to leave with the children under false pretence because he was threatening her - and I remember at the time adamantly telling the mother to not let the children visit with his family (or at the very least, to stay parked across the street the whole time). We could totally see where it was going, but she trusted her in-laws. They played on her emotions and her guilt. Well, lo-and-behold, just like we feared, they ended up kidnapping the children and driving them cross-country to hand them over to their neglectful, drug-addicted and abusive father. Once the kids were in his custody, there was nothing the police could do because he had just as much right to them as she did for lack of a formal separation agreement. The kids were traumatized from the kidnapping and being literally locked in the house so that the mother could not have access to them. In the end, she was awarded primary custody but it took several months to get that sorted out through the legal system.
It's difficult for good people to imagine how dangerous bad people can really be. We have a strong instinct to trust and downplay bad situations, especially when it's inconvenient or when it can appear to others that we're over-reacting. JD comes off as someone who is a huge people pleaser, and who always put others' needs ahead of her own. She was the perfect target, sadly.
JMO, of course.