1 Throw her off a cliff. If she is a witch she will use her magic to fly and save herself. Burning the body isn't necessary as death from falling has shown she was not a witch after all.
2 Strap her to a chair and dunk her repeatedly into a river until she drowns. If she is a witch she will confess (she can't fly away here since she is tied to a chair). Once a confession is heard, execution by flames is the only way to destroy the evil soul. Otherwise she will reincarnate as a witch in another body.
Identification is obtained by pointing your finger at the ugliest old hag in the town to blame after something bad happens such as the crops doing badly that year.
Official Book of Witchcraft, 1588.