Can my mother sue a fast food chain for an employee assaulting her?

A couple of days ago my mother and a friend ordered food at the drive-thru (or whatever you call the little stalls). The employee in question brought out their food, but the drinks were incorrect so she was asked if she would fix it, which she proceeded to do. When she had brought the drinks back out, she tossed one of the drinks through the window at my mother (big mess) and walked back inside, so my mom followed her. Inside, she requested for a refill, which was denied by the employee and after some words, my mom flung what was left of the beverage in question at the employee and walked outside toward her car. The employee then pursued her and, outside, apparently "drop kicked" her in the back of the head and proceeded to kick my mom all over her body. Thankfully her friend was close-by and ran to break it up, followed by the employee fleeing back inside and my mom going home. Thus, my question is: Can my mother sue the fast-food company, for the assault by their on-duty employee?