How did Dona Tina find out who told the police that Luismi was involved with the Witch's murder?

Yesenia has no idea how her grandmother Dona Tina knows how she had been the one to inform on Luismi. But in the moment when she sees Dona Tina's face for the first time after Dona Tina has heard the news about Luismi's arrest, Yesenia is absolutely positive that her grandmother considers her to have committed a major betrayal.