@bendmeoverbackwards
My observation, from your posts, is that DD3 is still very much able to manipulate you and twist you around, that you are still very enmeshed in her world view and favour her to the detriment of her siblings, especially your eldest DD as she dislikes her so much. I’m not sure that approach is doing DD3 any favours at all, I’m afraid, and the way she has behaved towards your DD3, and indeed her own father, has been utterly abhorrent.
I would also observe that anything DD1 does “wrong” is viewed quite negatively, whilst DD3’s transgressions are viewed with understanding and even kindness. There is very clearly favouritism towards DD3, who gets to behave absolutely appallingly with very mild censure, at best, and you wonder why DD1 is withdrawn and says she “doesn’t care anymore”?
My suggestion would be that your eldest daughter doesn’t trust that you are actually going to put her needs first, or even place them equally alongside DD3’s. She doesn’t think that you will believe her if her sister complains about her behaviour or accuses her of doing something. I think she probably picks up on the wider family dynamics, not just her youngest sister’s feelings towards her. So, I’m not surprised she is fairly uncommunicative and monosyllabic, if I’m honest. Add in someone who is introverted (and possibly has ASD, according to you), and I think you are having trouble seeing the nose on your face, so to speak.
Your eldest child is quite clearly a quiet person who prefers to keep things to herself, and certainly sounds like has traits that would be consistent with autism but obv nobody on a forum could diagnose her from that. You make allowances for DD3, accept her differences, but cannot seem to do the same for your eldest. It baffles me that you can do it for one, but not the other- even though you admit you think DD1 may be neurodiverse.
You say DD3 seems to lack empathy because she didn’t say anything supportive to your DH about his mother- but has she shown support in other ways? Not everyone is good at expressing things the way they want, but it sounds like she did visit her with DH recently- that is possibly her showing support in a way she feels manageable. Judge her in the round, not just in what she says (or doesn’t).
Also, if she does have ASD this might be an area where she struggles- verbalising her feelings and thoughts. You aren’t even sure DD3 said anything to DH (you “think she might have spoken to him about it”)- but you haven’t felt the need to clarify whether she did /what she said. Why then, are you so negative about DD1’s lack of appropriate response, given that you weren’t that bothered whether DD3 has or has not been supportive? You hold your children to very different standards, despite recognising both have their own difficulties.
You and DD2 sound quite harsh in your judgement towards DD1. It’s possible she picks up that she is not especially welcomed by DD2 and detested by DD3. It’s not a family/home environment that would make me feel comfortable and emotionally safe to be open about things that are hurtful or feeling able to be free with my feelings and thoughts. Then add in a mother who is easily manipulated by the sibling who detests her, who has in the past allowed that sibling to behave appallingly towards her (and I’d agree with her, elements of your dd3’s behaviour towards her sister do sound abusive) and even defended it to some degree- and I think I’d be keeping myself emotionally very closed off from my family too, for my own emotional well-being.
I’m not saying DD1 is perfect- she’ll be as flawed as the rest of us- but I suspect some of the closed off/aloofness may be a defence mechanism on top of her natural tendency/personality.
You have hurt your daughter, damaged her trust in you, and your relationship with her, with your past behaviour and ongoing (though sounds like to a lesser degree than previously) enabling behaviour of your youngest daughter.
How do you fix it? You take a long hard look at your family dynamics, you address the imbalances, you take time to rebuild the trust by being consistent in showing the changes, you show your DD1 you appreciate where you were wrong- and hope that over time it is enough to repair it.