tenyearsafter.....I know it is heartbreaking when family members do this on a regular basis. She must truly love you if she hasn't starting shunning you thus far. Be glad of that!
The Watchtower Society is a sub culture and, like most cults, have done an excellent job indoctrinating their followers. The older witnesses, like your mother, should be pitied in a way. IMO, they are truly brainwashed and this is a seriously harmful condition to be in mentally and spiritually. Why? Because, like being hypnotized, there have been triggers mentally implanted to stop them from hearing with hearing ears or seeing with seeing eyes. In other words, their ability to think clearly and rationally has been hindered or taken away completely and replaced with JW doctrines. They look at it as a theocratic struggle every time they talk to you, their family members that have left the organization.
They equate leaving the org as a death sentence, and when they talk to you, they feel fear and frustration that you have chosen to leave. Rationalizing that they are doing God's will by cutting you off, helps some of them deal with this fear and frustration.
They rationalize this by using various scriptures. (They have about 15 - 20 that have actually become memes, imo.)
They use Ephesians 6: 10-13 as their excuse or justification. It is one of the scriptures the Society uses to program their behavior and response to conversations like yours.
"Put on the complete suit of armor from God that you may be able to stand firm against the machinations of the Devil...."
"....take up the complete suit of armor from God, that you may be able to resist in the wicked day and, after you have done all things thoroughly, to stand firm."
So, you see, tenyearsafter, you're from the Devil and must be resisted .... she must button up tightly her complete suit of armor against you. But she still loves you. Speaking as a mother, just tell her: "I still love you even if you are brainwashed and that won't change." Then give her a big hug.