My mother.
I shall try and keep to the important bits of her life, and relevant bits.
My mother had a pretty awful childhood. She suffered abuse from her 'father' from a very young age until she was adopted by her mothers younger sister at age 5. She obviously resented her mother for letting this happen to her and never really forgave her.
However, now both 'parents' are dead. SHe is picking up family friendships - she has 6 sisters and a brother. She also has a half brother on her fathers side who she is getting on well with. My mother has spent many years being angry about her childhood and is learning to let go.
The thing is, i KNOW for a fact that her father was NOT her biological father. My adoptive grandmother told me as much. Unfortunately she too has passed. She knew that he couldnt have been her father, because of dates, by all accounts her mother was a bit of a floozy (forgiveable, my mother was born just at the end of the war, and it must have been very stressful for everyone, I wouldnt judge or mention it) Her half brother is not actually related at all, and she only has half sisters.
She still carries anger and resentment.
would it be better to tell her what i know, or let sleeping (or dead) dogs lie? would knowing that it wasnt actually her father that did this to her make her feel any better? would she just wonder who her father was? - and there isnt any way at all to find out now, be worse?