An attempt to clear Raoul by telling the superficial truth must involve terrible risks, and might at any turn enforce a choice between full confession and falsehood.
Dorothea could not bring herself to lie, even heroically; and there would be no heroism in lying to save herself.

On the other hand, the thought of a forced confession--it might he before a tribunal--was too hideous.

No, the suggestion had been a mad one, and Polly had rightly thrown cold water on it.

Also, it had demanded too much of Polly, who could not be expected to jeopardise her matrimonial prospects to right a wrong for which she was not in truth responsible.
Dorothea loved a hero, but knew she was no heroine.

She called herself a pitiful coward--unjustly, because, nurtured as she had been on the proprieties, surrounded all her days by men and women of a class most sensitive to public opinion, who feared the breath of scandal worse than a plague, confession for her must mean a shame unspeakable.