It is Lucie who hears the echoes of the footsteps but she has a firm belief that these echoes are positive and they have no negative effect on her. The way that she views life, even after the death of her son and the incredibly hard times she has faced remains positive and so the echoing footsteps too are positive in her eyes.
Yet they are meant to represent the marching steps of the revolution that has begun in France as the working class has finally thrown caution to the wind and decided to bring down the aristocracy. The peasants have stormed the Bastille and are killing noble Frenchmen as fast as they possibly can, their blood is running freely.
The noise of the footsteps reaching Lucie is perhaps a symbol of the great power of the revolution and that its effects will be felt not just at the Bastille but also in London and other faraway places as the common people have finally thrown off their shackles and risen to fight.