I have seen her nod her head several times when there was no reason to do it - and I haven’t watched her much.
“nod her head ... no reason to do it...”
Exactly - that is the cover up move for when she can’t help it.
I would bet that she never did this in the past. No doubt past videos of her over the years will NOT show her constantly nodding; this would most likely be proved to be “new” behavior.
Perhaps someone could do archived video research that shows otherwise but I suspect this is a recent phenomenon specifically done to cover up the involuntary bobble.