Construction coordination and organization in the absence of the client

Good day, the following situation occurred. In the extension/renovation, the shell with exterior facade and roof is already in place. Now the builder has dropped out and the female client without any craft experience and exact knowledge has to complete the construction. My question does not initially relate to the financial challenge, but whether there is a kind of construction supervision that can explain what possibilities exist for realizing the ideas and that takes care of coordination and alignment with the craftsmen. You find nothing under construction supervisor and with construction companions, only experts for damage prevention appear who check the trades. What is such a person called and how expensive would something like that be approximately? Thank you for helpful answers.