A soccer mom is driving her 75 year old grandmother and her 9 year old daughter home after the game. The grandmother and daughter were both in the back seat and both were wearing their seat belts. A car ran a red light in front of them, causing them to t-bone that car on the passenger side. Fortunately there were no serious injuries, but the grandmother did sustain several rib fractures. The mother, daughter and driver of the at-fault car were shaken up but unhurt. What are some possible reasons that the grandmother sustained rib fractures while the other victims did not?