I just wanted to take a moment to offer you some support. Please don’t worry so much about this. I was “the daughter” in the exact same situation. My parents were just like you (as you described yourself and your husband). After three years of living together, my boyfriend and I got married in a civil ceremony. My parents chose not to attend. My husband and I have been together for what will be 30 years this summer. We couldn’t be happier and our marriage has always been strong. We have a wonderful family (one daughter). We are both agnostics, and always have been.
My parents, too, were perplexed that they didn’t know I was struggling with my faith those many years ago. The reality is that, although they did their best to raise me in good Catholic tradition, I never really believed (even as a child). I went to 12 years of Catholic school. Not only do I not have the faith, as an adult there are many things about the Catholic Church that I cannot support (the typical things most agnostics find they can’t support). It is against my value system. My parents are strong Catholics, and very devoted to their faith. They live their religion. They did nothing wrong. They did everything right, as parents who wished their children would embrace the Catholic faith. As an agnostic, I have my own, equally strong set of beliefs.
My parents have 7 children. All but one married. Several married in the Catholic Church. I am the only one that hasn’t been divorced. It is ironic, isn’t it, given the fact that they were so against the relationship and (civil) marriage?
Anyhow, I just want to encourage you to keep your relationship healthy with your daughter. Do your best to understand that she may just not believe in what you believe. It doesn’t make her a bad person. And don’t worry about her “ruining her life”, like I have heard a lot of people do in your situation. She can have a fulfilling, wonderful life. My parents accept me and my husband. We just don’t discuss our differences with regards to religious beliefs, but we do respect eachother’s choices.