She could sue the robbers, if she can find them and thinks that suing them is a good idea. She can also sue the employee who set up the robbery. However, the restaurant/store is not liable and she cannot successfully sue them: the law is very clear that an employer or business is 1) not liable for the criminal acts of third parties (the robbers) and 2) not even liable for the criminal acts of other employees (e.g. the traitor), since such criminal acts are not part of the job and are beyond the scope of employment. Basically, if A robs or attacks B, B can sue A--but she can't sue someone other than the criminal, such as her employer, C, or the owner of that space (if it was rented) D.