Ami,
I understand. You feel there is so much cruelty to compensate for, if you are responsible for your mother's character.
Hon, she came first. She and her character were well formed by the time she had you. You were just fighting your way out into the earth's air from the spiritual universe.
When you have these thoughts, don't judge them morally (good-bad) so quickly. Try using beautiful-ugly. When you have ugly feelings, thoughts, or impulses, I think you just need to breathe in and out, quietly saying this word to yourself until they (and your shame about them) pass: mercy
This is what you can give yourself, and it spares you the fight. Nothing to struggle with, when there is mercy.
with love
Hops