I think, when faced with evidence or suspicions of a beloved son's wrongdoing or, there are two kinds of approaches for mothers.
1 The first kind seek to address the problem, to face up to it and encourage their son to face up to it, work on it, overcome it and make amends. It is gruelling and often it is a long haul. It involves emotional honesty, actual honesty, and investment of time and family resources.
2 The second kind effectively wash their hands of it all, 'can't cope', pass the problem onto others, and/or tells the son he can do what he likes as long as she never has to see about it or hear about it - 'don't bring it home'. Seen often as a 'lower class' dynamic, it is in fact prevalent in the upper middle and upper classes.
Throw Philip, Charles and her background into the mix, and it was #2 all the way for queenie. She strikes me as a woman with supreme agency when she wishes, but who is weak in the face of confrontation with the men she loves.