Doc , what questions do I ask?
It would be best to develop an issue that she has with the religion. WHY is she inactive? Was she treated badly or unjustly by someone? The Elders? Or is she inactive because of YOU? It's a bit surprising that her JW family/friends know she is living with you (for SIX years) without the "benefit" of marriage, yet they have not reported her to the Elders for fornication which would result in her being disfellowshipped. This would almost be the certain outcome, UNLESS she was never baptized as a JW, and is simply an inactive "unbaptized publisher". She would even have lost that status after not reporting FS hours for 6 months.
So........it would help to know what her "official status" is with the Church.
You could admit that you want to further examine her religion -- learn more about it. Why does she think it is the "true" religion vs the both of you looking for a church you could both agree upon? You could offer to begin attending some meetings WITH HER at her family's Cong so you could learn more and meet the JWs. If she's a baptized JW, I think she will run away from that idea as it would result in grave consequences and likely being totally shunning by her family/friends.
There are a multitude of issues that are problems with JWs. It would be best to capitalize on an issue that she has, if you are aware of such. Some of the most common serious issues that help people to awaken are:
The pedophile problem. -- JWs have ridiculed the Catholics for years about their pedophile issues in the priesthood, yet JWs are now facing the same issue. There have been dozens of cases filed against the WTS that have been "settled" with a "gag order" to avoid further publicity. The Candice Conti case is the largest single award for child abuse, and it is primarily the WTS that is being held accountable. The WTS has refused to appear when subpoenaed in recent cases, resulting in multi-million dollar awards. The JWs are just as guilty as the Catholic Church of harboring and protecting child abusers to avoid the bad publicity, all to the detriment to the abused child.
The failed prophesies.-- JWs have publicized the End of the World (Armageddon) multiple times through the years. Noteworthy dates that are easily documented are 1914, 1925 (when the ancient OT servants were said to be resurrected), 1975 (is the most dramatic example), 2000 (stated as "by the end of the 20th Century), and always very, very soon or "imminent".
Their rebuttal will be that they are not "inspired" or "infallible", yet they openly claim to be "spirit-directed" by God. They have claimed in the WT to be the equivalent of Ezekiel the inspired prophet who prophesied the destruction of Jerusalem. They claim to be God's only channel of communication; God's "spirit directed organization; etc. and yet, all of their "communication" concerning this destruction of this System of Things proves false. So, where is the evidence of God's Holy Spirit working with them?
JWs "preach" the imminent End of the World, but they clearly are not "practicing what they preach". The R&F JW is just living life -- (most) not concerned about the nearness of The End. They are building their 401K and building bigger houses and having babies, etc. If they truly believed that Armageddon was coming "tomorrow" they should be giving their whole-souled devotion to saving their non-JW family and neighbors. They are not. Most are doing their token 10 hours per month of driving around and sitting in Starbucks and knocking on the doors of empty houses. YAWN.
"Clergy" appointed by God's Holy Spirit -- They claim that the Holy Spirit chooses those who are selected to be Ministerial Servants, Elders,, and higher up "clergy". This is to support the fact that all JWs must follow the direction of these men without questioning anything -- because they are "appointed by God". They expect absolute obedience. These "leaders" are said to be the equivalent of Moses in leading God's people of Israel; etc and
compare those who question them to the wicked men who challenged Moses
and were struck down by fire from heaven. Yet, there are numerous examples of men being appointed who were pedophiles, adulterers, abusive husbands, thieves, etc. How can their claim be true?
Jerusalem destroyed in 607 BCE -- This is an important doctrine for JWs because it is the starting date that leads to their Hocus Pocus chronology for the claim that they were "chosen" as God's modern day Organization on earth in 1914. NO WHERE in history does anyone concur with the date of 607. All historians put the date at 586/587 BCE. You can't even find an published historical work on this issue, because it is not an issue with anyone (except JWs). So what? This totally destroys their principal doctrine of divine appointment in 1914 during WWI etc etc based on Dan. Chap 4 and the 2,520 years (day for a year prophetic doctrine). Trust me, most JWs cannot even attempt to explain this bullshit doctrine, and thus they now have a "smoke-and-mirrors" video on JW.bOrg to show to people to attempt to explain it. This isn't an issue for most JWs because they don't understand the doctrine and thus whether it is factual or not doesn't mean anything to them. (Deer in the headlights look is all your get trying to discuss it.)
Blood Transfusion Ban -- This ridiculous doctrine is gradually being allowed to erode away to the point that currently "blood fractions" are allowed, but accepting "whole blood" is still a sin. People DIE because of this doctrine. Children have died. JWs in the past encouraged parents to "steal" their children out of the hospital to avoid the child's treatment. No more is that the case. They encourage the parents to concede to the Courts orders and allow treatment and put the "guilt" on Caesar's Courts vs their own conscience. They no longer want the negative publicity of JWs sacrificing their children to this doctrine. JWs will claim divine guidance on this saying it "saved" them from getting AIDS from tainted blood. Thus God protected them from this scourge. There is an exhaustive rebuttal to their blood doctrine that has been written and published here as well as I assume it is likely on jwfacts. It's just another example of a totally BS doctrine that is claimed to have divine inspiration.
"Ban" on Higher Education -- A big issue to many is their hard line stand against young people going to college. They know that an educated person who learns to do critical thinking will usually see the fallacies of JW doctrine. They already lose 2 of 3 young persons who are "born-in". Of course, this policy cripples the opportunity for young people to achieve success in life. But those who have "hard times" in life are better candidates to remain JWs. They can find relief that it is not their fault that they are unsuccessful and struggling and are disadvantaged in life. No, it is Satan persecuting them. And, "soon" Jehovah will destroy this unfair "System" and they will be instantly rewarded with Paradise and wealth and and health and pet Pandas. In 1969 the Awake! magazine published the statement that this "wicked system of things" would come to an end before any young person could finish a college education. I'm one of those young persons. They were really hyping their prediction of the "End of the World" in 1975 at that time. Most JWs under 50 won't even remember that huge "prophetic" failure.
There is also the Flip-Flopping on doctrines; the recent money grab where the WTS demanded all Congs send them all of their excess funds; their demand for Obedience Without Question on all things; their belief that the UN is the Wild Beast of Revelation, yet they were a voluntary NGO member of the UN for 10 years until that was exposed in the media and they instantly resigned. Many others will contribute ideas here too.
You CANNOT go into a discussion in a "shot-gun" fashion with all of this info. You also are best to find some "source" of info rather than an "apostate" site. Someone at work trying to warn you; or some family member or friend trying to help you learn, etc etc. Any JW (prob even your GF) will just poo-poo any "apostate" info as "sour grapes" and lies. Best to find that issue that disturbs her, and examine it. Let her help you to explain away the questions.
Six years together means you both obviously have a huge investment in your relationship. You can't easily just chuck it all away. I would bet that she thinks she has been compromising on her chance of everlasting life FOR YOU by having this "immoral" relationship with you, but by getting married she will be able to "get right" again with God (and the JW network). You will become the persecutor when you demand that she compromise on this vs her willingly compromising on it. It's a trick bag.