Hi Hippy,
I've name changed for this. First of all its not your fault,your mum was an adult before you, she should have tried harder at being a better parent. You weren't a horrible child, as you say she has no social skills so she was probably quite inadequate in dealing with kids' behaviour and its easier for her to blame you than look inwards.
She sounds very similar to my mum, and like your dad mine also stood in the background and didn't say anything to stop her. My mum has been shrieky and verbally abusive since I can remember, and even physically violent with me until my mid twenties. I used to always blame myself, and sometimes still find myself doing so.
She had me very young (19) and acts in a very immature manner even in her mid fifties. I don't think she really wanted to be a mother, and she has no maternal qualities. I wish I had a mother I could phone every day and have a normal conversation with, but there is always a frosty and critical undercurrent when I speak to her, she makes it quite obvious I am a hindrance to her in some way. Though she is very close to my sister, who is also very aggressive in her behaviour. She rarely asks after my ds which I find very hurtful.
She would, still does, go months without speaking to me for no apparent reason, during which time I would vow to cut her out of my life, then she would phone me out of the blue as though nothing happened. Then, if I refused to do something she would scream and shout. If I try to challenge her behaviour - for e.g. when she phoned to tell me she was going to start a fight with my v nice aunt at my wedding - she weeps and wails and gets my dad to to give me into trouble and tells everyone what a horrible daughter I am.
It is only recently, since I've had dc of my own, I've been able to start saying "no" to her as I've been frightened of her for so long - and I'm 34 with a highly responsible job!
She hasn't spoken to her own sister for years after falling out with her over a trivial matter and has divided both me and my sister too - she didn't even tell me my sister got married recently! When I plucked up the courage to ask why she just started screaming at me, saying "no one loves me", and blaming me. I am now convinced she has a personality disorder.
While pg with ds I bumped in to my mum's business partner. They've always been best friends, or so I thought, but on conversation about babies she told me she was distancing herself from my mum socially and hadn't approved of her parenting techniques.
I was stunned, because up til then I thought it was my fault, there was something about me that made her behave like this. I realised this possibly wasn't the case and have started to become a bit more assertive and limit how often I see her, and on my terms.
Anyway, sorry this is so long, I've never really spoken about this before - should probably have posted on "toxic parents" thread! but just wanted you to know I know how you feel. Maybe try and keep your distance and accept she won't change.