Poison for the Fairies (1986)

In 1965 Mexico City, Fabiola, a wealthy yet lonely schoolgirl, befriends Graciela, a young orphan girl who has an unhealthy fascination with witchcraft. Fabiola is convinced that she, herself, is a witch by Graciela, who then uses the fear that she’s put into her new friend to get Fabiola to carry out her orders. As their games grow more serious, the two girls find themselves involved in murder.