She had the less motive to resist, resistance would make so much noise. Therefore Kitty surrendered.

It was a movement of vengeance upon Milady. D’Artagnan believed it right to say that vengeance is the pleasure of the gods. With a little more heart, he might have been contented with this new conquest; but the principal features of his character were ambition and pride. It must, however, be confessed in his justification that the first use he made of his influence over Kitty was to try and find out what had become of Mme. Bonacieux; but the poor girl swore upon the crucifix to d’Artagnan that she was entirely ignorant on that head, her mistress never admitting her into half her secrets — only she believed she could say she was not dead.

As to the cause which was near