Wow I'm with you missyouthful, my mum has done that my whole life but I hadn't heard of a name for it. It took me years to affirm to myself that my childhood did happen the way I remember and even now she will say I imagined something or I'm "obviously more delusional than she thought".
Don't know if it was the same for anyone else but there has been times where my mum would admit for example the sexual abuse that occured, she would cry and get very remorseful for not doing anything about it, then a week later when I was struggling to deal with it she would say things like "you don't even have any proff that I happened, you probably made it up" or "you need to get help because of your need to lie" lol and the good old favourite "stop making up things that didn't happen and making it sound like your childhood wasn't perfect"
I just came up with the conclusion that her denial had convinced her she was right because the truth was too hard for her.
Sorry for the long post! Just got me thinking...