Hi C.~
In answer to your questions in order:
A. Yes, you may find your fears are realized-- or not.Cross that bridge if and when you come to it. If her friends' families do not allow her to develop those friendships, that may be a hard experience, but there is still a lesson in this about tolerance. Your daughter has parents who are practicing tolerance by allowing her to attend the church, and if the parents of those children are discouraging the friendship, this could be an eye-opener for your daughter. If she *does* end up believing this religion, you can let her know that there are other churches who worship Christ in a more tolerant way. It's a very valuable lesson to learn that a *church* or a *congregation* is not God or Christ, it is only ONE manifestation of worship, nothing more or less.
If you are concerned about her receiving backlash from other parents not wanting their kids around you and your husband because you are not followers of their faith, I think this opens up another valuable conversation about fear and judgment. This is an opportunity to ask your daughter "what do you think the parents are worried about? What could they fear?" My guess (from your previous posts) is that you and your family don't spend a lot of time trying to freak people out by being 'other' (I don't know you, so maybe you do, but that's not the impression I get). So, if you aren't getting into theological debates with the kids or drinking and dancing around them, I think it could be a worthwhile conversation: judging based solely on assumptions is only hurtful. It will hopefully teach her to be thoughtful in considering 'difference' between herself and others.
B- No. I don't think it is wrong to let your daughter attend and to let her learn about another way of living. I'd feel differently if your post had read "we love it! It's like free babysitting!" :) I don't see that. I see you trying to support your daughter in the best way possible by not being fearful and letting her figure out some things on her own. I would offer to your daughter that if *she* wants to tithe, you could help her figure that out from her allowance (that's part of being a Christian, tithing that 10%, so it's another realistic aspect for her to consider). If she doesn't have an allowance but is feeling uncomfortable about tithing, talk to your husband and see what you both feel would be reasonable to send her with. (You might also ask her "What do you think this church spends the money on?" and see what she comes up with. Do they have missions going which require money, or is the money used to support a behemoth building and fancy services? I think that would be a sticky point for me if the money is used to line the pockets of the pastors instead of being put to good works.)
For what it's worth, my husband and I are both secular humanists (I'm more Buddhist-influenced than he is) and we wonder when our son will question our family's beliefs. One thing we plan to do (and have already done) is to discuss religions when the topic comes up and to offer good information which is respectful of those who do believe. We are careful to avoid generalizations, but to remember that people's faith matters deeply to them even if we don't believe in it ourselves. As he gets older, we will offer books/materials on comparative religion. Both my husband and I experienced our own journeys before coming to the conclusions regarding spirituality that we did (and I do believe I have a very rich spiritual life). I also expect that my son will have his own path to follow, all we can do is be supportive. Good luck to you and your family in doing the same for your girl.:)
PS: Riley has great points regarding individual church theologies. I hadn't considered the 'hateful' side of things (don't know why, as I left a church which vilified gays) -- if that sort of intolerance is at hand, yes, find a new place for her to try out Christianity at! So, yes, sit in on some services and find out what their message is.