I don't think it's possible to just switch off our caring about people. Even people who may have been monsters.
This woman raised you, and even though she crapped that job up completely? There's still going to be a natural attachment that develops because she was a significant figure in your life, especially since it was during your development. The fact that part of you still cares is a testament of your character as an empathetic human. It's a good thing, so even if she doesn't deserve it, it's a good quality to be able to have had.
There's also potentially a lot of grief here that will make a simple switching off of the Caring switch harder. You should have been loved by her, and had a beautiful relationship with her, but you missed out on that. There's a lot to grieve about this relationship which complicates the caring issue.
I think preparing for feelings of guilt is going to be tough, but maybe try and approach this the same way you would approach tackling any core belief. Challenge it when you notice thoughts or feelings associated with it, remind yourself about what is and isn't important to you now. And maybe instead of trying to fight the feelings off (which too often turns them into even bigger, nastier monsters) give yourself permission and space to have those uncomfortable feelings, feelings you don't want. It's a bit like, "Oh, there's that empathy/guilt for the old witch again. Don't want to feel that way, don't need to feel that way, but I do. No big deal. Next thought...".
Feelings about her? Don't undermine who you are now, what you value or believe, and they don't actually give any sort of measure about what you've had to survive. They don't reflect her, or what she deserves. They're just leftovers of having spent a lot of time with this particular person during your formative years. So they might be unwanted, but they're perfectly natural and healthy even (on your end - doesn't seem much healthyness at her end).
So, if you had a thought about her and realised "Oh, there I am caring too much about her again", what would happen if you simply acknowledged that thought, and then consciously let go of it? Instead of fighting against it ("Get away you dreaded caring thoughts and feelings, I don't WANT you!!"), just acknowledging that it's a pesky thought that you don't really want but is habitually, naturally there anyway? Would it become a little less powerful maybe?
If anything maybe congratulate yourself - the woman doesn't deserve a second of my time but here I am, decent enough to have cared all these years anyway." Without the struggle against the thoughts, just gently reminding yourself that they're ok but you don't need those thoughts anymore, a lot of the distress may be taken out of the equation.
Either way, it is a distressing situation. I'm sorry you're dealing with this. Be gentle with yourself.
