I know how she did it. She established an endowment that was meant to be administered by Coppola.
Honestly, GF3 is a violation of sense anyway, but this example, for me, is the most outrageous. If something is absolutely impossible, that is. He would never wish to have something in common with this woman, and definitely he is no fool to send his children to the only person in the world who will most surely employ any means to make them hate him for life. Of course, he would never let her come close. I really don't think Michael would like have a son looking, thinking and singing as a sacrifice of low quality castration.