Again you miss the point. She wasn't the gun owner. She was just related to him. So it is used as an excuse to attack her politically. She was not home, it wasn't her gun and a thief broke the law. So why do you insist on blaming her? It is not at all like a kid skateboarding down your deck stairs. The thief was committing an illegal act so property rights and their responsibilities don't apply. Legally the rifle could have been anywhere in the house and the thief would still be at fault. All her son did was tempt a dishonest person with an open garage door.
Simply doesn't matter. Legally, her son put her at risk. Legally she is responsible for what and who is in her house. I'm not saying it is "fair", just that it is common for a family member to put the household at risk stupidly.