I think Mrs Maloney is the lamb as she was innocent. Mr Patrick Maloney is in the wrong and i feel that Mrs Maloney should be applauded for her actions as her husband was insensitive towards her. Even if he wanted to leave her, he could have said it in a more sensitive manner, such as maybe going out for dinner and explain the whole situation to her. If he had done so, Mary would not act so rashly and maybe, she would accept it that he wanted to leave her. I believe that Mrs Maloney had murdered him as a crime of passion, and she was in a state of shock. Although she is wrong for murdering him, it is quite acceptable as she did not want Patrick to betray her. She wanted him to be hers as you can tell she loves him very much by reading the text. For example, she waited all day for him to come back home and it would be impossible for her to live without him. When he came home, she leaned forward to kiss him, hung his coat for him and insists that she made him his glass of whiskey.
So, i conclude that Mrs Maloney is the real lamb who was slaughtered and that it is pardonable for her not to be prosecuted as it is a crime of passion.