In reference to paragraphs 47 and 48 of "Lamb to the Slaughter," what are Mary Maloney's motivations?

I believe these are the two paragraphs in question.  

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.

Mary Maloney's motivation is her unborn child.  Mary has just hit Patrick over the head with the leg of lamb, and Patrick is lying dead on the floor.  Mary knows what will happen next in terms of police, detectives, and an investigation, because Patrick is a law enforcement officer.  Mary also has a fairly good idea of what her own personal punishment will be.  She is unsure of what will happen with her baby.  Mary is currently six months pregnant, and she is unsure if she would be jailed and sentenced while pregnant.  Mary isn't willing to find out, and her motherly instinct takes over.  That's her motivation.  She is protecting her child, and she is willing to get away with murder to do it.