Her coachman, whom she questioned, had not seen anyone answering the description his mistress gave him of the wizened figure of the little Frenchman.
Evidently, therefore, he had been ahead of her all the time.

She had not dared to question the people at the various inns, where they had stopped to change horses.

She feared that Chauvelin had spies all along the route, who might overhear her questions, then outdistance her and warn her enemy of her approach.
Now she wondered at what inn he might be stopping, or whether he had had the good luck of chartering a vessel already, and was now himself on the way to France.

That thought gripped her at the heart as with an iron vice.

If indeed she should not be too late already! The loneliness of the room overwhelmed her; everything within was so horribly still; the ticking of the grandfather's clock--dreadfully slow and measured--was the only sound which broke this awful loneliness.
Marguerite had need of all her energy, all her steadfastness of purpose, to keep up her courage through this weary midnight waiting.
Everyone else in the house but herself must have been asleep.