I'm so sorry to hear this. All I can offer you is this... I had a JW mother and a non-believing father. My mom kept me away from my Dad and I didn't see him until I was 18. Now I'm 30 and believe it or not, I finally have a relationship with my Dad. If you would have talked to me at 18, I would have spouted off the VERY SAME CRAP.
Those aren't her words or her feelings, because 10 years ago I could have written that same letter VERBATIM. She has been told over and over things that she is accepting as her own beliefs.
I do think the reason why she said she felt sick when she had to visit you, is not because she didn't want to see you, rather she was feeling all sorts of anxiety about her own conflicted feelings. She has to go visit her Dad, but the tension and stress is making her sick. The pressure to conform is sooo great.
This is what I suggest you do. Write her back a very loving and kind letter. Telling her that she truly is the best daughter in the world, complement her on her sweet nature, her smarts, etc... just lots of complements. Tell her how proud of her you are, how you genuinely love the daughter she is. Tell her how you always made sure she was taken care of in her childhood, that you always loved her and still do and it would break your heart if you weren't at least a witness to her wedding. Although you understand that she might not want you to walk her down the aisle, out of respect you do wish to attend your own daughters wedding. Tell her that ever since she has been a baby you have wanted to see her grow up happy. Tell her that any communications, visits, etc from now on will have NOTHING to do with the religion. You don't need to discuss it any further, but you gave her life and you are her father and you think she needs to respect you as her father and at least keep in touch.
Try to make it NO pressure, she is under a lot of pressure as it is.... but continue to reinforce the fact you LOVE her. At 18, she is desperate for love, she wants to be accepted, she wants to fit in... but no one is going to love her UNconditionally except for you. Make sure she never has to feel anything different.
At 18 I knew nothing, here I am 30 and finally have myself together. I didn't leave because anyone showed me literature, scandals, etc... I left because I didn't believe it anymore. Give her time. Don't preach to her anymore, she's getting plenty of preaching from their side, she will find her own way. If she wants a car discuss it with her, tell her that if she needs a car then you will be happy to provide her with one, but she has to respect you as her father.
Keep the communication there, even if it's just a trickle. She is going to remember every detail of how you handle this... if you throw up your hands and give up on her, then she is going to feel abandoned and only sink deeper into their mire.
Good luck... and I truly am sympathetic. I know my own Dad loves me very much. He actually gave me away in my wedding in 2004, my JW mother didn't attend and it was sooo very wonderful.
