attack occurred wednesday at alverta b. gray schultz middle school in hempstead , new york .
mother annika mckenzie , 34 , breached security by getting into building .
believed math teacher catherine engelhardt had touched her daughter , 12 .
mckenzie allegedly attacked her , with students joining .
one of them was allegedly mckenzie 's 14-year-old niece .
mckenzie and the niece were arrested at the scene and charged .
engelhardt was unconscious for several minutes and taken to hospital .