How about just not tell the child?
What do you mean? The very first thing you should do when a child first learns how to talk is to describe to him how he was conceived.
As you well know, anytime you bring a child to the doctor, with a problem, the first question they ask is: "Is there a history of such and such in your family?" Genetics plays a big role in medicine today. And even if the family manages to keep the paternal donor's information a 'secret', the child will one day be an adult and find out.
The decision to pursue this course of action is simply an act of greed. In this woman's desire to have a child, she has taken the "it's all about me" route with no concern for the offspring.