My grandmother was charming on the surface but had the ability to quite vile and spiteful when it suited her. Thus she made my mother's life hell at times (her daughter-in-law). When confronted with the actions of one of her other sons (my uncle, if you managing to follow this
) she went into complete denial and claimed my mother was delusional. She wasn't; my uncle's actions and behaviour were a matter of record.
Sometimes you have to fight fire with fire; it's self preservation.