I explain her needs and desires do not necessarily align with his and that she must try to notice his (I describe them like do you hear he is yelling because of XYZ). This is largely futile. Because she notices he yells but doesn't understand why. He's only 3, so he mostly plays parallel (normal for his age).
I also describe the circumstances of the situation. Usually it is before dinnertime. So I explain right before dinner isn't a good time to play together. Because they trigger each other. So it is a good time to play solo and respect each other's boundaries. At that time they're hangry and difficult, so often some drama isn't avoidable.
Unfortunately some triggers cannot be avoided. They have to go bath sometimes, and we settled for once a week. He hates to wash his hair. Our daughter had same, as did I.
