Welcome losthusband! Yes, you're going to get mostly anti-witness information here, but that's ok because if you want pro-witness information to compare it to, you can speak to the JWs who are calling on your family. Win.
My mother began studying with the witnesses when she was about 23 years old. Her big question in life was "Why does God allow suffering?" The witnesses offer an answer to this question. When you take this answer on its own, it can be satisfying and relieve the stress of trying to reconcile a loving God with a cruel world.
The trouble is, that when you examine EVERYTHING they teach, the answers do not add up. Witness teachings are like a house of cards. When you pull out the doctrines and beliefs that can be proven untrue, the rest of it comes tumbling down.
What I liked about being a witness as a teenager, (and what attracts many people to cults in general) is the feeling of having some great and special insight into the major issues of the universe. I pitied people who didn't know what I knew. I didn't have to worry about the future because there wasn't going to be a future in this world. Imagine how much stress that relieves for a teenager! When you don't have to be anxious over school and career and future family because you don't believe this world will go on long enough for those things to be an issue.
When someone begins studying with the witnesses, there is an initial period of friendship called "love bombing." She will be welcomed into the kingdom hall and treated like someone very special. What girl wouldn't be motivated by that? As time goes by and she either makes a commitment by getting baptized or stalls in her progression, the love will fade. If she commits and she's lucky enough to be the kind of popular, outgoing person that people are attracted to, she will have friends for as long as she remains loyal to the jws. If she doesn't make a commitment, she will find herself friendless. Either way, the specialness wears off.
Instruct your daughter in the skill of reasoning. Make sure she understands logical fallacies and how to recognize them. Make it a game (try offering a dollar for each one) to discover them in everything she reads.
Encourage her to become involved in activities with other non-JW teens. Sports, picnics, volunteer activities, book clubs--find fun and fulfilling things to occupy her mind. Make sure her life is filled with opportunities for education, friendship and fun. And offer emotional support for the anxiety she is no doubt facing on the cusp of adulthood. She has a lot of life-altering decisions ahead of her. Becoming a witness is a way of escaping from that. Help her to know that she doesn't have to escape because she's got you as a support for these major decisions.
Do not forbid her from studying. This will feed into the jw persecution complex AND natural teenage rebelliousness. Tell her you support her, and you want her to take in enough information to make a wise, informed decision.
As far as telling your partner she's nuts-don't! If you were looking into a new religion/career/hobby/long-distance carrier/etc would you want her to tell you there's something wrong with YOU for the choice you're considering? Make it clear that you respect her interest in this subject and her right to freely choose a form of worship that's right for her.
Go the opposite route and take an interest in it with her. Let her know that you're skeptical and want to be like the Bereans by "making sure of all things" from the Bible. Offer to do extracurricular research with her on the internet.
Remind her of purchases you've made in the past. Do you take the manufacturer's word that their product is the best? Do you compare it to products from other manufacturers? Do you read reviews from people who have purchased it? Do you read only the good reviews or do you read bad ones, too? Why is it useful to do this?
Never make it sound like you're attacking her or the individual JWs who are calling on her. In fact, don't even attack the beliefs. Just question. Say, "I find it odd that they JWs teach this, when the Bible says this. Why do you suppose there's a discrepancy? Which source do you think is more trustworthy?"
Here is a resource for questionable topics with JWs.
Do not draw away from your family or fight them as they take an interest in the JWs. The JWs are teaching them that this will happend because they have the truth and Satan is out to get them. Do the opposite and draw closer to your family and take an interest in what they're learning and what questions they have. Make sure they always know you are on your FAMILY's side rather than just on the opposite side of the witnesses.
Good luck and, again, welcome!
