Who should a mom blame for her son's accident if anyone?

Say you know a woman Ms “T” who is in a very high octane job, she often has to pass on events her son did. One of which was an important soccer tournament her son wanted her to attend but she had major conference to attend and sent her son to the tournament with her 21 year old cousin. On the way they were hit by a drunk and her son loses a leg. Should she beat herself up for not taking more time to be with her son? Would she be right to blame the cousin because he was the driver? Should she just vent at the drunk and lay it all on her doorstep? Should she be worried her kid will put the blame of his lost leg on her for being too busy with work?