What is Mary's conflict in "Lamb to the Slaughter"?

Mary's conflict is to
protect her unborn child no matter what. She is surprised at her ability to despatch her
husband so swiftly, but it is the though of the child within her which focuses her
attention on covering up the crime. She first begins to consider the future for them
both-

It was
extraordinary, now, how clear her mind became all of a sudden.  She began thinking very
fast.  As the wife of a detective, she knew quite well what the penalty would be.  That
was fine.  It made no difference to her.  In fact, it would be a relief.  On the other
hand, what about the child?  What were the laws about murderers with unborn children? 
Did they kill then both-mother and child?  Or did they wait until the tenth month?  What
did they do?

Mary Maloney didn’t know.  And she certainly wasn’t
prepared to take a
chance.

It is this
primitive urge to protect which enables placid, devoted Mary Maloney to ensure that her
husband's murder becomes the perfect crime.