Let's add one more thing to your comment and then ask you a question.....let's say that Mrs. VD danced or turned Westerfield down for a requested dance the night her daughter disappeared.....do you still think her mother had no effect on the "events" of the evening? With their fancy garage, my guess is Westerfield knew exactly what went on in that garage.
I think or possibly believe Mrs. VD's grief may be real, but not for the reason some child loving parents might think....Mrs. VD may be living a personal hell for having turned down Westerfield's request to dance or for ignoring all the warning signals (flashing lights) of that night.
I don't think the final chapter is written on this thing yet!