Even with your sister having a suspended license and driving in an unregistered and uninsured car if the other person was at-fault in the accident according to most state laws they would be responsible to pay for the damage they caused.

If the police are involved it is likely that your sister will be getting a hefty fine or much harsher penalties for driving a vehicle without a license, insurance or registration. Since the accident was done in a parking lot, which is generally considered private property, the police might not want to become involved.

When your sister is ready to get insurance follow this link.