Is Mary a sympathetic character in "Lamb to the Slaughter"?

The great thing about stories is that each person has a different reaction to characters! Let's look at both sides. How is Mary presented both as a sympathetic character and unsympathetic.
First, sympathetic. Mary is, at the beginning of the story, shown as a demure housewife waiting for her husband to come home. She is presented as sweet and doting; the kind of wife many men might like to have. She fixes his drink and is quite to try to adjust to whatever her husband seems to want to do for dinner.
Unsympathetic. Though it was not premeditated, Mary ends up committing murder when she clobbers her husband over the head with the leg of lamb. After realizing her horrible accident, she takes care to cover her tracks, going so far as to have the policemen eat the 'evidence' - the leg of lamb. This part seems deliberate. Can a murderer be sympathetic?
Reactions may vary, but it's interesting, too, to look at the motivation. Her husband leaves her unexpectedly, and she is pregnant. It is after her husband has told her that he is leaving that she knocks him over the head with the leg of lamb. To some, this may be justification for her actions. She still seems the same sweet Mary at the end, despite her actions.

Absolutely! And that's why the end of the story is so interesting!
Mary is sitting at home like a dutiful wife, waiting for her husband to come home from work. She cares for the home, cooks dinner, and tries to make everything perfect for her husband. So it is a surprise when her husband comes home at the beginning of the story and says, "This is going to be a bit of a shock to you, I'm afraid. . . . But I've thought about it a good deal and I've decided the only thing to do is tell you right away. I hope you won't blame me too much." The reader assumes that the shocking news has something to do with divorce or having an affair, some news that is unsettling to Mary. That is why she is in a daze when she grabs the leg of lamb, and she is still in a daze when she whacks her husband over the head with it, enough to kill him. It was not premeditated murder, but she did have the wherewithal to make up an alibi afterward so the police would believe her when she said she didn't know how her husband died.