My next sister is precisely 1 year and 11 months younger than me (she hated being called 2 years younger!) We were together for much of our childhood, and had the same upbringing, going to the same school and daily life at home. We have of course a lot of memories in common, yet we also have memories that we are convinced are true, that the other sister says never happened , or that we had misremembered the same occasion. It is partly, I think, because you have your own special interests, so you remember something that appealed or affected you more , so stands out in your mind. Another person would remember a different part of the same occasion. So I have always liked coffee in cakes or anything and she liked marzipan . So we would remember the same party together but the cakes that we liked would not be remembered by the other one. In the same way if the police ask for details from witnesses they remember different things. So when you talk to another person and they remember different details of the same time, you see each other as either liars or wrong, and then you want to convince them that you are right, so you can put more and more emphasis on that thing and it can become a battle to win., so you keep reliving the battle and going round and round and getting now where
I was quite bright, but as the eldest I was expected to take my sister with me , and I was always told to take care of her etc. You are the eldest, dont let her go in the road , scuff her new shoes, or whatever. If we did anything wrong or came home late etc. it was always "you are the eldest, it is your responsibility. Someone of your intelligence should know better" So that responsibility made me feel anxious about things and feel I had to make sure everyone was safe and ok and so my sister and I can agree about everything that happened at a party or an occasion, but she felt comfortable and laid back and hadnt got that attitude . That can show that two people can experience all the same things but react in a differnt way.
I think you will really not get far trying to stop her way of thinking and she will believe her own version. So there seems to me to be a choice of which way you go. If you feel this is beginning to wreck your total relationship, as she will keep saying her version is true and you will feel so upset and angry at the way you are portrayed. Then maybe you might either try to speak to a counsellor, either on your own, who you could explain how this is making you feel , or if your daughter is willing to have some joint sessions, if she prepared to try and look at things with someone who is outside the situation, Or, a couple of other suggestions, when she starts to talk like this ,choose some non judgemental reply. So you might just say "well we have different memories of this" where you are clearly not agreeing with her , but you are not telling her she is wrong either. If you then change the subject or close that conversation in reality by saying something like Im just going to put the kettle on etc etc. . If she insists on going on trying to get you to accept her version, I think you could also consider just not replying to any comment on her words and literally move away, going into another room or just remember you need to get something or go to the bathroom. Hopefully you might have a close friend who knew you she she was young, who you could go to , to be able to speak to someone who could confirm your version. Then for a physical thing, when she has left and you are on your own with no one about, then think about what she said and thump a cushion to let some of the anger out!! I hope that things improve for you , just dont let her spoil your pleasure of today with making you concentrate on the past which you cannot improve by whatever you do now. I would make a resolution to let this fade and spend more time trying to enjoy today.