If you answer the door, that's a good start. But it's easier to make sense of the Bible in a discussion with JWs if you have a NWT, try to find to answers for yourself using the cross-references and the Index at the back of it. Also, sitting in the meetings with a notebook and pen helps. As well, if you're at a meeting, you are welcome to arrive 15 minutes early and stay at least 15 minutes late talking with them and having them show you around. I hope these tips help. After all, Keep on ASKING, SEEKING, and KNOCKING (Matthew 7:7-12) is a good way to get the answers we're looking for.
Yes, yes, but the above doesn't answer your question, does it? This advice would probably render a continuation of the "answers" you've been getting. Not answers, really, just, "Come to the Kingdom Hall, take notes, and KEEP ASKING."
Of course, if you are a witness, as your mother is, the admonition to "keep asking" can get you into a lot of trouble. When I was going to the Kingdom Hall, and first heard this-that Jesus was not my mediator, first I was taken aback. I reread the scripture that says that there is ONE mediator between God and man, and yep-it said JESUS. But, now, I was being told that the 144,000 as a class-read Governing Body-were my mediators. Everything that I believe and the judgement as to whether I am a fit human being must go through this class. They will determine if my prayers are sufficient, etc. I knew I was reading something in the Bible that didn't fit with what the WT said ......BUT!!! I knew enough NOT TO ASK QUESTIONS as that would definitely mark me as one who is disobedient, and a questioner of DIVINE TRUTH. My husband was an elder-I was even afraid to speak to him about it very much.
I know that this "new light" troubles many witnesses. If I were you, I would not get off into many other questions with mom. I would continue to ask mom to research this question--the elder husband too. How is this so? Who specifically is your mediator?? Through whom should you pray? How are the 144,000 your mediator while on earth?? Why did Jesus say that there was ONE mediator, him, when clearly the WT says differently? Can they show you how to answer the question using only the Bible?
Please let us know what you find out.
Just a side note--I think the JWs still think that each creative day was 7,000 years long and obviously this does not account for dinosaurs or ancient plant life. Some time you could ask about that.