Crikey, I would never come on mumsnet asking for help for parenting difficulties. You are asked for details of the problems, then you get accused of being negative about your child. You mention punishments are are almost accused of child abuse. Dare to say anything about your own relationship with your parents, and all the armchair psychologists pounce about “repeating patterns”, and I knew that Radio 2 should never have done a piece about “scapegoating kids”......
So sorry OP. You come across as a caring mother at the end of her tether. I think your DH, as you are aware, is exacerbating the problem. To say to your DD about you having “favourites” is a truly toxic remark. It’s not just undermining you, it could feed into, or create anxieties for your DD. It’s turning you into the “baddie”, and creating sides. He has to stop this to move forward as you know, although I really don’t know how to make him.
I think what may be happening now is things are spiralling. So, both your daughters behaviour, your DHs response and communication with you has now gathered it’s own momentum. So, maybe a deep breath and call a stop. Is it worth saying to him that you need to discuss things with him. Set aside some time and explain how you feel, that you need to agree on some course of action, It is very easy for him to sit on the sidelines and criticise you, but he needs to recognise there is a problem and that you need to agree a solution. I would be very firm that inconsistency and him undermining you is bad for your daughter. Telling her you have “favourites” is not just horribly unfair on you, it is damaging to her. Try to get an agreement he will not do this again. If this doesn’t work then maybe some outside help?
I think it worth you making an appointment with the school. As others have said, it is SO common for children with any learning/processing difficulties, or with anxieties to hold themselves together at school and then go berserk at home. Try to see if there are any friendship/academic issues. Are there things she is good at, and things she finds really hard. The school may be able to help refer you for informal family therapy or a counsellor re the behaviour. A GP could refer your DD for counselling, or for assessment if you think this may help.
Putting a stop to the spiral, I would say, maybe the same with your DD. My 10 yr old DD was pretty awful at 9. It was like she would get furious for no reason, be horrid and be totally unable to back down. Some things I found that helped. When I felt I’d lost it a bit and didn’t know what to do, I waited until she was in a good mood and calm, then chatted privately in her room, just saying that there was a problem which we needed to sort, identifying behaviour which wasn’t nice and then both of us talking about what might make it better. What I think really helped was identifying to her that she was growing up so maybe she could be more helpful and I could trust her more to do stuff. Giving her responsibilities REALLY helped. I think it made her feel good about herself. This could be whatever you think your DD might like. My DD was keen to start cooking meals, baking cakes, supervised, but her doing everything. I bought her her own hair dryer, she started doing tricks training with one of the dogs. If your DD is difficult about eating dinner, maybe agreeing a week’s menu and getting her to help cook? I also chat to her about “my day”, asking what she thinks about things, or what people had done. Sometimes we spend hours in her room ‘tidying’, but in reality just chatting and joking. She loves animals so sometimes I’ll find a funny dog video on you tube and go up to her room to show her. I suppose it’s trying to have “good moments”. I know this is all pretty obvious, and I’m sure you do it anyway, but, with me, it was about doing MORE of this stuff.
Also, the knowing when to back off. My DD would radiate “leave me alone” behaviour. When she was about to “blow”, I’d back off, or I’d give time where possible. Sometimes even say, “OK, I can see you’re cross so you’ve got 10minutes before we go”. Giving warnings too, so, “OK, 10 minutes before tea/bed/leaving for school.
I tried the charts, withdrawal of privileges and rewards, but it didn’t seem to effect any change. I do still impose “consequences” for bad behaviour though if needed, although the last 6 months or so has been so much better. If my DCs keep me waiting for some reason, then if it’s significant, it comes off their time in the evening. So, if you're half hour coming down late for tea, there’s now no time for TV/screen. If you’re late going up to bed, then no time for your book and you’ll have to go up early tomorrow, so again, no time for screens/tv. Having said that, it’s rarely needed because I try to keep them “on side” and they both (10 and 12 ) are still read to before bed, which they really look forward to - they pick a book and get a chapter or so each night.
I do hope things improve for you. I think it must be very hard with your family not helping either. These things can make you feel so alone.