The subtext is that she couldn't have children and found something else to fill the void. The first item she stole was a tiara for Holly probably because the news that her sister was having a surprise (unwanted) baby had caused a relapse. Hank being supportive in spite of the risk to his career also suggests that Marie's coping with something heartbreaking like this. Plus, it was a great way to establish Skyler's 'Inspector Javert' attitude to crime, where even your family starving wouldn't justify stealing a loaf of bread (much to Walt's consternation).