Mary McMillan was attending a Parents’ Visitor Day at Camp

Mary McMillan was attending a Parents’ Visitor Day at Camp Cougar where her daughter Rachel went to Summer Camp. While there she was sitting on a bench near the sandbox area talking to a little boy named Timmy. Timmy’s mother, Carol Mann thought her son Timmy was being teased by Mary, so she picked up a rusty bucket of sand and threw it at Mary’s head causing severe cuts, destroying her contact lenses and needing a resulting blood transfusion. 

Carol was there because her son Timmy was also a Camp attendee and she had been asked by the owner of the Camp to volunteer to to keep everyone in, or near, the sandbox safe. She had been assigned that duty at previous Parent Camp Days. Mary’s daughter, Rachel, witnessed the incident,t and has been diagnosed with PTS stemming from that witnessing.. Mary wants to sue the Camp and its owner for the damages that she and her daughter sustained due to the acts of Carol Mann.

QUESTION: 

Mary wants to take the Camp and its owner to court. Under what theory could she recover from Camp Cougar and its owner for the acts of Carol Mann? What would Mary have to prove to the court to be successful under this theory?