My mare lately developed a very unpleasant habit of shaking her head (pretty violently) when she's mad/unhappy about something. Which she does in field pretty often (for example when my other horse invites her to play and she's not in mood), but now tries it out when taken out too. Like when I walk her to the ring and she's not in mood to work she keeps trying it. And when I'm taking her back (and she doesn't want to go back to the field too ) she does it. It doesn't look like she's trying to avoid the work, but she's definitely showing her frustration with weather, snow, wind, whatever else she can find.
I tried backing her up and moving her rear, but as long as I stop and go forward - she does it again. Last time I took a dressage whip with me and when she started all this fuss just smacked slightly on upper leg. She quit I should say. The problem is I usually don't keep the whip when I just walk them from/to the field/ring. So curious if there are any other ways to deal with this behavior?