Often, we idealize our family relationships to the point of overlooking situations that hurt us, keeping us unconditionally attached to them. However, we are beginning to understand that the mere existence of a family bond should not force us to remain in environments where we do not experience love or even where we are hurt.

The situation faced by the protagonist of this story is extremely complicated because it is about a person who is important in his life. Here are some tips to help deal with any conflicts one may have with a relative:

The first thing the dad in the story did is an excellent way to address the problem. Taking a step back, leaving the scene, and letting the feelings that have impacted him calm down a bit will prevent a major argument.
Making a list of his feelings and what he needs to say to his sister, to have a mature discussion and make decisions, is a way of looking at the bigger picture.
Trying to find the root of this decision. Perhaps she has done something similar before or a situation has occurred that hints at her unpleasant behavior toward the child.
Finding a quiet moment to talk about the situation, and then think about what might have led to this painful decision. It is also worth asking up front why she did it.
After listening to her and expressing your feelings, you will be able to make a decision, not necessarily at the moment, but you will be able to analyze if it was a mistake, a misunderstanding, if it is something you can work on so that it doesn’t happen again and also so that the wound she made can heal.
By the way, a study by the University of Cambridge found that being at odds with your siblings can create a better adult life for the both of you.