Zugz:
Thank you for posting your letter; you are right that it is for your peace of mind.
You are dealing with a cult; cults can be religious, and cults obtain almost complete control over members. You have made the break from the cult of Jehovah's Witnesses and now want to make clear that break to a remaining member of the cult, in this case your mom.
I had a "friend" I wrote a letter to also, just so they would be aware of my stand, and the response was typical JW speak and jargon, parroting the same inculcated beliefs I had heard all my life. I mentioned to them why it is I knew everything they were thinking and going to say, yet they knew nothing of what I was thinking or saying to them? They didn't know how to answer. Perhaps it's the same with your mom, she does not know what to say except what she has been taught to say (that's what their books are for, to teach you how to think and what to say (ref. Reasoning from the Scripture)).
Critical analysis and thinking are not Witnesses' forte. That is not welcome or encouraged, so when you no longer are a member, one cannot expect current members to see or think as we now do, at least not immediately, but maybe something will spark the synapsis and trigger the process of ratiocination in their minds.
As my former friend does, members seek the reassurance of other members and the comfort of being in the cult to justify their thinking, seeing everything around them as supporting their skewed vision, not even considering it in some other way. They need to know how the WTS sees things before they can decide what to think.
Unfortunately I was taught that it is a fight, it was a struggle, I needed to defend the truth, to uphold the truth, to pummel my body (and mind); all teachings that put one on the defensive, to be negative about life (the world is out to get you, same with apostates), and that I can't accomplish anything worthwhile on my own, without their direction.
You have made the final break and can now begin your life. Whether you mom ever does only time will tell. You don't need her permission or the Society's to continue to live.
Welcome.