I'm no expert on this but my 84 year old MIL now has dementia yet is as sweet and kind as she ever was but she finds it easier to be honest about her feelings and to say what she's really thinking . Before dementia, if we asked her something as simple as whether or not she thought the soup we made for her dinner needed more salt, she'd spare our feelings by saying "oh no...it's perfect" then later she'd give it a few shakes of salt when she thought no one was looking. Now, she has no trouble saying she doesn't like or agree with something but she does it politely and with kindness still because that's who she really is, deep down.
In my opinion, the display you saw at your last visit with your mother, came from someone whose dementia is making it impossible for them to hide the ugly person they are deep down inside (who knows what might have happened to her as a child?). Still, it sounds like you were emotionally abused by your mother and yet as is often the case, you still loved her, kept trying to please her and on some level may have blamed yourself for the difficulties between you.
Even though your mother was "gone" a number of years ago, it was unkind and unfair of the family not to tell you she had passed. None of this should have happened to you and you were quite right not to ever go back there.
There are many who have left the JW's yet carried around a sense that they themselves were to blame for the religion not working out for them. The only way for them to get past those haunting feelings and to heal is for them to investigate and truly understand the flawed doctrines and hidden past of the organization. Even as flawed as some of the views JW's have, are , they wouldn't have condoned your
mothers disapproval of your pioneering simply because it wasn't "where
the need was greater" and all of the other nonsense she came up with to brow beat you with.
The only way for you to heal now is to get to the point where the young girl still left in you absolutely believes and understands that children don't have to be anywhere near perfect in order for their parents to treat them lovingly and no matter what, you shouldn't have been treated so badly.