Well, sometimes a bit of positivity help.
My girlfriend is a born-in in a pretty hardcore JW family. After we began dating, we talked a lot about religion. Today she is out. It can work, but it all depends on her. If you are going to make an attemt, you must study their theology HARD, you must know it better than them. you got to make her agree to what lying means, and you got to be able to show how they have lied again and again and you got to show her support and love so there is a chance she will take it into her hearth. It wont be easy, but sometimes it can be done.
I would recommend you to get her to agree that she should study the religion before she get dipped and have to buy the theology, lock stock and barrels, for all her life. Then make her agree to do some of the following 5 studies:
1) Have they allways been honest in what they have written?
2) What are their history? What do they believe, how did they come to believe it and has it changed?
3) Is the blood doctrine consistent and build on the bible?
4) Is 607 really the right year for the fall of jerusalem?
5) What is mind control and what kind of groups does it apply to?
but before the studies, talk with her if she will be willing to study non-wt puplications. Talk to her about what it means to have the truth, if it is okay to research it, and if she should have a good answer to all rational, serious questions you ask her.
Also, make sure you know where the bodies are burried in all 5 questions, and make sure you make her commit to the part of the WT positions you can blow out of the water, it will make it harder for her to ratinalize it away later.
eg. in case of the history lesson, try to see if you can make her commit to something like: "Well, jehovah selected them in 1914 because they was preaching that jesus would return shortly" (in fact, they thought he had returned 40 years prior!) or "If someone said that so and so would happend in a specific year, for example that armageddon would begin, and they also said they was Gods channel of communication, and it didnt happend, yah that would be a false prophecy according to the bible".
Read everything she gives you vigeously. The best would be if she want you to write to Bethel or talk with some elders. If you pick your fights right, you can trash them pretty good. They will respond in a predictable manner, and you can prep her for that to.
but first and foremost, show her you love he and you really care for her. You are asking her to give up a very big part of her, and admit that she and all she know are dead wrong. Its not an easy thing, and even if you succeed there will be elders crawling up your assess trying to DF her, and her family will likely act shitty even though the are decent people.
Oh and by the way: If you are an atheist, i would seriously recommend you to have a good talk with her about how rational the whole "God-loves-us-but-he-is-gonna-kill-us-all-over-a-talking-snake-and-some-magic-fruit"- thing really is. The christians here will disagree with that approach, but talking about how silly that whole concept is actually made a great impression on my girlfriend.