Long story short. I have been a SM for 10 years since I left my BS at 18 years old in another country to be with my husband, I have a late in life ASD diagnosis and am damn sure my partner is also autistic (he doesn't want to know). My SD was 3 when I arrived, her BM bad-mouthed me to her from that point on for years. It has been some kind of hell on and off the 4 to 3 nights a week she stays. The first 6 years I had no marriage when she was in the house. Tantrums if her BD even spoke to me, expected all of his attention all the time. Took a lot of convincing of him that this was not OK. The only thing she ever said to me was where is dad? I have cooked, cleaned, cared, driven her to school and back, been pleasant, been interested, played games, y'all know the drill.

Every so often SD would do something wrong, nasty or naughty, like kids do. If I bring this to my partner's attention, he instantly gets enraged and argues that I don't know what's going on and am probably wrong and he 'won't take sides' (WTF- making sides in the process). This kid has laughed me out in my house with a friend over my clothes. Stuck my toothbrush down the drain, hidden stuff and been cruel to animals. She just says I didn't do it and BD says oh but It's terrible to be accused of something you dint do, maybe she didn't. If she gets called out,  she cries for herself, It's happened twice in 13 years. NO consequences BD believes the bullshit mostly.  I get gaslit and triggered (I had a seriously bad childhood), and shouted at if I bring it up.

She is now 13 years old, and It's stepped up a level. I have chemical sensitivity and am allergic to the wash product her mother uses. This has been an issue for 8 years. A year ago her BM agreed to change product but SD still comes to our house in some old clothes full of it sometimes, so we ask her to change and  wash she arrives.  I have spoken to her calmly about it 3 times, and she seemed to understand and certainly did not say anything about it. it was once that I was literary choking with my throat closing and had to tell her to get changed while barely able to talk. She said to her dad that I was bullying her at that moment (WTF!!)  He said to me that I was being over the top  I was scared I was gonna stop breathing. :(.

When I was sick with fever and covid a couple of weeks ago which SD brought to the house (BM says she doesn't have to take tests because she doesn't like the stick in her nose FFS). She decided to to go into conflict about it, sat in her chemical clothes in the same room as me and started to cry. I thought ok this kid has been sick It's probably not really about this and tried to repeat what I had said on the other 3 occasions. She just denied any knowledge of our conversations, and I was in a crap place feverish and being affected by the chemicals, so I just called it out as lies. So she ramped it up screaming 'this is the worst thing in my life!' (having to wash and change) 3 days later her BD says she didn't say that, when he was sitting there when she did.. She tries not to wash at all. Its a teen phase right? Although in this case I am starting to think it's passive aggression.

Now she  said to BD doest feel comfortable with me in the house and that she thinks I don't like her when I have done nothing but support and accommodate her for 10 years. 

Well now I don't feel comfortable with her in the  house and look up against her coming back every week. I have to put on a pretence, mind what I say and what I do so as not to displeasure her. I don't get brain rest from this. I don't think she is capable of empathy, I have put my partner onto conflict resolution skills, doubling and mirroring and Moreno's developmental theory and kudos to him hie is trying to learn. 

I find SD totally self-centred, her BP's lives revolve around her when she is in their homes. She has never been interested in me and before she learned to mask her feelings was obviously unhappy every time she heard something good happened to me and vice versa. Has never once instigated a conversation with me or asked to hang out or play when I have done this thousands of times for her, and she does do this with her BD.  And TBH I don't like her that much, I can think of other kids I would rather live with. I do however have empathy and give her a hug if she needs one, meet her care needs etc. What is there to like? She is also having problems at school getting on with other kids and has only made one friend in high-school. She says she's intelligent and they are dumb. Her BM and BD both say she is special and sensitive. I call BS and narcissism being passed on.

She says that she can only talk to her BM and no one else in the world. She was sharing her bed up to age 11. I call Follie a deux. Her BD has no idea what's going on in her head. She learned at age 4 that to get out of trouble she just had to shut her mouth and leave benefit of the doubt and then wait a week til her forgets everything.  To get his sympathy she just has to cry. She cries when she is angry to get her way. He still calls her baby names and talks to her like she is 6 years old often, like 'the kiddies in school'.

Thanks for listening to my rant.  I have never had an argument with my partner that has not been caused by this manipulative child. I have convinced him to seek psychological help for both their anger issues and inability to resolve conflicts directly or practice empathy skills. I suspect that if he tries to get her to a therapist she will resist and the BM will not want it being a therapist refusing historically violent and entitled headcase herself. I am at the end of my tether.