She could not.

She was a wise woman-- a generous and loving-hearted woman; still, in that self-contained, solitary existence, which had been spent close beside her, yet into the mystery of which she had never penetrated, and never would penetrate, there was a nearness to heaven and heavenly things, and clearness of vision about earthly things which went far beyond her own.

She could not quite comprehend it--she would never have thought of it herself -- but she dimly felt that the earl's judgment was correct, and that, strange as his conduct might appear, he was acting after that large sense of rightness which implies righteousness; a course of action which the world so often ridicules and misconstrues, because the point of view is taken from an altitude not of this world, and the objects regarded there-from are things not visible, but invisible.
Cardross appeared next day--not at home, but at the Castle, and was closeted there for several hours with the earl before he ever saw his mother.

When he did--and it was he who came to her, for she refused to take one step to go to him--he flung himself on his knees before her and sobbed in her lap--the great fellow of six feet high and twenty years old--sobbed and prayed for forgiveness with the humility of a child.
"Oh, mother, mother--and he has forgiven me too! To think what he has done for me--what he is about to do--me, who have had no father, or worse than none.

Do you know, sometimes people in Edinburgh -- the Menteiths, and so on--have taunted me cruelly about my father ?" "And what do you answer ?" asked Helen, in a slow, cold voice.
"That he was my father, and that he was dead; and I bade them speak no more about him." "That was right, my son." Then they were silent till Cardross burst out again.
"It is wonderful--wonderful! I can hardly believe it yet--that we should never be poor nay more--you, mother, who have gone through so much, and I, who thought I should have to work hard all my days for both of us.