Why does Mercedes come to see Monte Cristo? what is the result of her visit?

The Countess de Morcerf (Mercedes) visits Monte Cristo and pleads with the Count to spare her son. She cries that she too has suffered from pain of loss of Dantes, her lover. She did not realize that she had married Dantes' enemy, the man who had had him incarcerated. When Monte Cristo agrees to let Albert live, he tells her this means that he will die. He is surprised when she thanks him for sparing her son. She calls him noble and great hearted.