Helping to understand

Hi everyone. This is my first post on the forum so I'd just like to say I'm happy to be here and hi. I'm actually writing in the hope of help, to learn and for advice regarding something not immediately connected to me, but to my Father's wife (step-Mum). It may be a bit long winded, but I'll try and keep it short! I'm also writing this not as a criticism of her, but to understand. My Dad's been in a relationship now for I think about 14 years with a woman who was adopted, although I'm not sure at what age she was adopted. I've never had a great deal to do with her or her family or indeed even my Dad's side of the family as my Mum took the marriage separation/divorce and Dad's re-marriage quite badly, so split loyalties came into play when me and my sister were younger. However, within the last couple of years as we are now older, we have tried to embrace both my Dad and his wife into our lives. However, things have not gone smoothly. I first noticed things were a bit strange when I used to go to their house. I know that my Dad's wife is in charge of photos and other jobs in the house and saw that the house is flooded with photos of her daughter, some of her son, herself and my Dad's side of the family. In the bedroom, there are probably a dozen or more photos of her children when they were younger, almost like a shrine. Her daughter seems to have most photos in the house and, coincidentally, her daughter sings/performs as my Dad's wife also used to do. I was asked by my Dad to bring some photos of myself and my sister. I did do and not long after had them handed back to me by his wife, who had made no effort to put them in the house but seemed quite content they had just been uploaded onto the computer. In the meantime, she would tell me about how lovely it would be to have a photo of my Dad's family to put in the house, so knew something was going on. A few years ago, when my sister was at university, she shouted down the phone at my Dad after feeling let down about something. During the call, she insulted his partner. She was wrong to do so and knows it. However, having not even met his partner and not even spoken to her before, it was clearly just a way of lashing out at my Dad. But that phone call appears to still be being used against my sister to this day (about 10 years later) and my Dad's wife still seems to be holding it against her. What we find doubly confusing is that my wifes' daughter was apparently very nasty towards my Dad when they first met. But that is now forgiven and forgotten by him. Since then, it appears that both of them have only ever looked for the worst in my sister, although I strongly suspect that my Dad is holding onto things from the past because his wife can't let go. It has ended up that my sister now doesn't see or speak to my Dad. I was sat with my Dad's wife one night and, after a few drinks, she cried a little and told me that me and my sister have never let her into our lives. This came as a surprise as I thought she understood that it was difficult for us as children to do so because of the situation between my Mum and Dad. During the same conversation, she also told me something which I wont go into, but it was regarding my sister and simply wasn't her place to tell me. It all came to a head one day when she told me that my Dad and her are thinking of moving abroad because my Dad's brother is moving, her Mum is ill (now passed away) and her children aren't going to be in the area. But there was no mention of me or my sister, which I found upsetting at the time. Please bear in mind that she had said all of these things to me, with no one else in the room. I felt I had to raise my feelings with my Dad which took a hell of a lot for me to pluck up the courage to do. I later received a phone call from my Dad's wife denying to me and my Dad what she had said. My Dad and I arranged to meet and talk, but he never showed and I haven't spoken or seen him since that day (about a year ago). From my experiences, I feel my Dad's wife has been lashing out at those she feels don't fully embrace her. I know she has had anger management in the past and has even told me she holds grudges and she also shows an almost fascination with my Dad's quite large family. I was hoping someone may be able to help me understand and whether I'm right or barking up the wrong tree! Do you feel her adoption is playing a big part on her life? Does this also impact and influence partners of people who are adopted? Thank you so much in advance.