I myself am a Christian and I praise my mother daily for taking me to church, Sunday school, surrounding me with people of faith, and living by example. She established a clear expectation of wrong, right, and faith when I was very young, so it was never a question for me. But she was also careful to not get legalistic with me and encourage me to have friends of other faiths, appreciate other ideals, and never be judgmental because someone didn't share my point of view.
I can imagine you are hurt by your daughter's choices. I've watched a progression of this with my SIL, she's now 21 and a pretty self assured Atheist. Most of the family is terribly bothered by her choices...for good reason. Granted, my husband's family is very loosely Catholic and didn't do a lot of definitive religious teaching or church going with the kids, so it's understandable to me that she would question faith because she didn't get a particularly strong foundation. I pray for her all the time because debating, and inciting her to argue or get defensive do nothing but push her away. I once told her that I respected her for questioning and wanting to seek out her own place of faith or no faith as an adult, but that fundamentally she needed to know that I disagree with her and always will and if she wants to talk about it, I'm here, but otherwise, we leave it alone.
I think the expectation of your child to attend church with the family is reasonable, she is still a child and needs to abide by the rules of the house. You also have a right to monitor her friendship choices and activities, again, she is still a child. But, she's also on the road to adulthood and is going to question and ultimately determine her own beliefs. Best thing you can do is live by example, don't shove it down her throat, and give it up to God in prayer. Have confidence that you have laid the ground work as a parent and God will do the rest.