I'm sorry that you lost your mom, and even though I don't know you or your mom's thinking, and maybe you didn't even know her thinking before she died, please don't judge her too harshly. Sometimes people develop different mind-sets when they are ill and death is imminent. On the other hand, it doesn't matter what your mom thought or believed; it's what the future holds that's important.
I am a firm believer in the millenium which will be a blessing to all people, including your mom. It is promised. What none of us knows is how and what is going to happen before we get there. 6 billion people being destroyed -- is just a musing taught by the WT. Many people of other professed Christian beliefs have different teachings on this, and all I can say is that we just have to wait and see.
Congrats on being a future grandmother!!