Des, I think you are believing what your mother is saying... somewhere down deep. You are NOT dirty, much less guilty!
DES, THIS IS
NOT ABOUT YOU! This is your mother's sick mind at work! If she's back on drugs, then you KNOW it's the drugs talking. No doubt she's paranoid. She's not in control of her faculties! Keep that in mind.
Tell yourself, "this is true; I am a good person. I am a good daughter. My integrity is intact!" Keep saying it over and over until it speaks louder to you than your mother's words.
I understand how it feels when none of your family will stand up for you. Mine don't either. I fight my battles all by myself. Always have, always will.
Wish my youngest would grow some balls, too! His wife comes on here, stalks me, tells lies about me and he does NOTHING! Says NOTHING!
My oldest daughter was abusing her boys. Jerry saw it, John saw it, David saw it, an ex DIL saw it. They did NOTHING! I did and they ALL turned against me!
Des, you have to stand firm in YOUR beliefs and not budge. You have to fight for those beliefs. One belief you have to stand firm on is that you are NOT what your mother is accusing you of! Her mind is sick. Your mind is HEALTHY!

I have faith in you!
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Psalm 119:105 Thy word is a lamp unto my feet, and a light unto my path.