Your mom is scared because she really believes that God is going to have to kill all nonJW's, including her own family members.
Jehovah's Witnesses have an unhealthy fear of God because of the lies they have been told by false prophets who produce religious literature filled with failed interpreted prophecies, constantly changing doctrines (read Ephesians 4:14 and see who it applies to), medical policies that have caused many of their followers to lose their lives prematurely, etc.
Your mom needs prayers asking that God start a good work in her like He did with you and your husband (Phillipians 1:6).
It was terrifying the the first time I attended to worship services at a church after I left the JW's.
I thought God was going to strike me dead on the spot when I pulled into the parking lot and saw the cross above the building.
I asked Him to let me know what to do and it was if I was being pulled against my will to the front door.
I went in and met my friend who had invited me and within 30 minutes inside I knew that almost everything I had been told abour 'Christendom' as I was growing up was not true.
It was as if God had pulled a blind fold off my eyes. I heard things about Jesus that I had never heard in a kingdom hall or read in a Watchtower magazine.
A lot of JW's would leave the cult if they had heard what I heard about Jesus during that sermon.
I think you may have opened a door for your mom with what you told her.