A Bolt from the Blue (S01E13)

It is nearly the end of Mildred's first year at Cackle's Academy & everyone is happy, except for Miss Cackle! She's short with all the students, particularly Mildred whom she threatens to expel. The girls soon learn that, it is in reality Agatha, Miss Cackle's evil twin, returned to take over the school! Now they must prove it to the other teachers & save the day! (Prime Video)