You are doing the right thing - but it is perfectly normal to miss her. And to miss what she could have been.
She can't - or won't - ever be the Mum you deserved. That's not your fault. And I'm sorry. No child deserves it.
You are entirely reasonable to keep away and to be missing/grieving what you should have at the same time.
It's not a badge of honour to be able to switch off your feelings or to hate somebody - for that to happen usually takes significantly greater levels of abuse and neglect - which is just as sad for the person who feels like that.
I don't miss my mother - I miss having a Mum. On the rare occasions I've been forced to be in her company, I feel conflicted, as in some ways, I feel sorry for her life and how cold it is through her own choices - and pure contempt for how she treated and still treats people to get what she wants. I did miss her for a while after the rage from her final appalling behaviour subsided - but when I had to be in contact again, I realised that nothing had changed and went back to having nothing to do with her.
People who say you only have one mum aren't the ones who have abusive, neglectful or inadequate ones. Or they just haven't managed to break free from their own conditioning.
I would say to them 'True. Only one woman can give birth to you. Doesn't mean that if that one is unable or unwilling to be the safe, warm and loving centre of your childhood that you should continue to put yourself in the position of being hurt as an adult by them, though'.