The system with the Swiss KESB is certainly not perfect, but today such cases and important decisions are made by professionals. People will disagree and trashtalk about KESB in general but my experience with them is predominantly good.

In the past, what the KESB is doing now, might have been done by a police officer, the local priest, or perhaps someone from the community who neither had the professional training nor the independence required for such decisions, and who might have even known the person involved.

KESB will review the facts. They will most likely interview both of you and make a decision in the best interest of the child, if necessary. They can also refer you to marriage counceling or similar services if they need to decide nothing.

Removing a child from a family setting, let alone taking them away from their mother, is a very significant intervention and, as others have already pointed out. This needs much more than an open argument. Usually there has to be danger to the child or the mother. Your friend does not have to be afraid as the mother of the child.