My understanding is that jw's have the WRONG gospel. I believe the key in helping them to understand that is essential and one of the only ways to get through to them. It is biblical and they should find the assumption fascinating; that, wow, they could actually have missed something. And that throughout their future Bible readings that one question will always rear it's head and maybe one day have the veil lifted.
1 Cor 15:1-4 begins to say what the true gospel is.
Romans, the whole book, explains what the gospel DID. Romans 4 is very good.
Galatians does a good job of seeing that works, or the Law, led to Christ and that works are no longer necessary for it was all fulfilled in Christ.
Ephesians 2, and the whole book, does a good job of showing works have ended.
In the end, jw's do not truly believe down deep that they are loved by God. They feel they must do their best, do all the right things, be the outstanding person in the crowd and then be faithful to death to have the slightest chance at life. Their salvation is not guaranteed.
The gospel says they are loved tremendously and that through faith and not works they will be deemed as righteous and meriting life eternal. If they can ever see that it will blow them away. It did me.
They want the helmet of salvation. They want life. They do not feel worthy of it because none of us are. It is a gift!
The obstacle to seeing all of that to a jw is they feel that all that talk is only to the 144,000. They only have 2 places in the bible to come to that conclusion. One speaks of it in Revalation and it pertains to Jews who will be redeemed. The other is in reference to other sheep which refers to Gentiles and not the great crowd.
Have them prove that the gospel is not for them. That is what they are fighting. They are trying to prove that God does not love them. They will say all the right words, but in the end those are the things they do not have and are searching for. Love and grace and salvation.
I would recommend reading Romans with her. I think Paul's letters will get to the point a lot quicker. It will also show what Paul's good news was! Christ died and rose!
I will also share a sermon that I absolutely LOVE. I feel it is the epitome of life, our dilemna, and our salvation from ourselves. It is by Mark Driscoll from Mars Hill Church in Seattle. It comments about what the gospel is, and the two enemies of the gospel; idolatry and religion. The idolatry shows where we go wrong by thinking this or that will make us happy and it doesn't while the religion part really shows the error of jw thinking. I have listened to it over 20 times. I weep every time. It is the essence of my truth as I see it. I hope you like it and I hope it helps in seeing where jw thinking is wrong and how to help them see it.
Mars Hill Church - It is called, Examining Two Enemies of the Gospel. You need to look up sermons and then specials.
You can also get it on iTunes under Mars Hill Church. The sermon is entitled Examining Two Enemies of the Gospel or Creative Church Conference, the dates are 5/29/07 and 5/30/07. They are the same sermon. You can even see it as a video on their video iTune.
Sorry for going on so much about it, but I do feel that it is at the core of jw false teaching and how to understand them and how to help them.
Let me know how it goes. I am very interested in hearing about your experience.