An example of this can often be seen in genetic counseling. It is possible for the counselor to know that a married couple have a one in four chance of a child having a particular genetic disorder, but it will never be possible to state that if the couple have four children, three will be normal. Each child has its own individual one in four probability. These often, if not always, involve the assignment of blame. Those are the breaks of the game.
Uncertainty frightens people, regardless of age and stage, and clear causes provide comfort.
And if some of those causes relate to the attributes or behaviour of the individual, guilt is a likely result. In this case, we might even agree that she deserves to feel guilty to some extent. However, it is useful to remember that regardless of her behaviour - some of the blame must go to genetic factors, and living in Australia. But then, she must feel guilty as a parent in turn. In the present case, it is very difficult to imagine a way to tell Daryl that some of the cells in his blood are bad without him thinking that he himself is bad.