You have to face the reality that unless a witness is in the right mental place NOTHING you say will help them see the madness all that will happen is it will ring all their alarm bells and the focus will be on you and your apostacy.
Your mother is also in a position where she would have to face the fact that she has brought her children up in a destructive cult, that is a huge thing for her to face up to. She would need a degree of humility to accept that this is what she has done. No parent would want to know that they had harmed their children.
This is an occasion where less really is more. Telling her everything will accomplish nothing.
When I approached the subject with my mother I just said, I think the Governing body has lost it's way. This allows for the possibility that they were once correct and that things have changed. When she asked what I was concerned about I told her I found the focus on the GB disturbing and that Jesus and Jehovah were given much less prominence. Over time we discussed many issues and she agreed with many of them although she would never break free herself.
I understand the temptation to tell all but it is not a good idea. Witness tell new ones not to tell people everything all in one go because they know it just doesn't work Information dumps scramble the brain and cause shut down. This is a time when patience is required if you want to let her know how you feel without causing rejection.