Ok. So I've just today read through your entire two threads. What a palaver!
I was chatting to my teenage dd earlier and we were rambling on and I was saying that I don't think she's like me at all (can't recall how we got onto the subject) and she said that we are, because I'm stubborn! Not a trait I would ever have assigned to myself, but through the eyes of a child, perhaps I am.
You're not going to like this, but I actually feel really sorry for your Mum. It's like she can't do right for doing wrong. I totally get that she and your Dad in the past were giving more to your sister. But she needed it more than you do.
I for e.g. have a very well of brother. He will inherit everything (not that I plan on either parent dying soon). I have just accepted that as fact. With acceptance comes peace.
You don't appear to have accepted anything. You have written words saying that you do, but I'm not getting the feeling that you actually do. So I get the feeling that you may be, like me, as stubborn as a mule.
You say you understand PND, but nothing you have written shows me that you do actually understand it.
That your mother had to leave her children for 8 months must have been absolutely horrific for her. And again as your Dad said, at a time when there was no treatment really. Certainly no support.
I don't mean to be mean by saying this, but you sound completely self absorbed. While you have managed to round up a posse on here to spur you on, you haven't for one minute thought about how your mother is feeling. I have read statements such as 'I feel sorry for her', but that doesn't really come across in what you're saying.
I actually don't know what you want out of all of this, or why it has suddenly come to a head. You sound quite controlling and able to control your Dad and sister. Your mother is another story, which is why you probably lock horns.
You will never be able to change how your mother felt or feels. Point number one. You might have changed how she is acting, but you will never change how she feels.
Your sister seems to be the collateral damage in all of this. Yes, she may have had more handouts, but maybe she needed them.
All in all, it's a bit like if your Mum is the government, your sis is on benefits and you're the struggling middle class. You have no need to resent your sister getting 200 quid a month when you jointly take home 3800 a month.
It's the equivalent of asking the government to tax everyone at 20%, and to give benefits to working people too.
You seem fixated on your mother's abandonment but apart from saying you understand PND, you display no true understanding of it.
In short, when you point a finger at someone, look at your hand. There are three more pointing back at you.