My opinion about this, for what it's worth, and I do know the family well, is that EBC is terrified about losing Nigel as well. She is, even at her age, besotted with her husband, hence the kiss in the garage (that wasn't for the cameras - that is her genuine 'Gone With The Wind' approach to her husband).
She knows her son will now pay for his sins, and maybe part of her thinks he rightly should, but her approach to Nigel's (alleged) sin would be entirely different: he did it for the blind love of his children, in the dead of a short night when there was no opportunity to think it through, not with a panicked son demanding help and NOW. I think she is a woman in a lot of emotional pain, about to lose everything, including the man she adores more than anything, endured jungles and moved countries for. She would not want to go to prison and see where NBC may soon join his son. My opinion only.