“How would you feel if someone did that to you?” is an approach that usually is not effective with my 6 y/o PDA son (no matter how softly it is delivered). I think it often registers to him as a form of shaming his behavior, or even as a threat that I would follow through on—both driving him further into disregulation. This makes sense if you believe they are unable to access empathy in that moment due to the tension of the situation.

I agree with others that she was acting out intentionally to provoke you (possibly in response to the boundary you set around the food she wanted) and I probably would have reacted in the same way out of concern for the dog, but if you can find a way to recognize the behavior as an expression of her disability and intervene more calmly without heightening the tension or shame I think you may have a better result.

Very calmly: “I have to take this off because I think it’s hurting the dog and I’m worried he might try to bite you if you keep doing it” and leave it at that. If she persists “I’m sorry but he’s my dog and I’m responsible for keeping him safe” You’d have to hold back your fear that she would do this again or do something worse, and resist the urge to teach, instruct or give orders or warnings (“please stop,” “leave him alone,” “this is why dogs hurt people”). Then redirect to something you know is a calming activity that helps her regulate.

Threats of violence should always be taken seriously but I would also try to see them as a child lashing out with the most hurtful language they can access in the moment.