H.W.
Christian or not, a good therapist is a good therapist and one that won't be a good fit, won't.
I'll share a little of my experience: I'm a secular humanist and my husband is an atheist. The fellow we go to see from time to time is in his 60s (at least) and has a Masters of Divinity. I adore him. He's had enough life experience to give very good advice, understands what couples need for good communication and has never spoken to us about following commandments or buying into a 'church' belief/value system *because he is a pro*-- and he knows what we need. (We started seeing him, by the way, when we were committed and living together-- about five years before we got married--and he never once suggested that we conform to his beliefs or get married.)
My two other great counselors I've worked with are both Christian women and that has never been an issue that's come up; I've never felt uncomfortable about religion/beliefs with either one of them. Once again--they are professionals who care more about the clients getting healthy than validating their own life or choices/beliefs. Truly the impartial counsel, all three of them.
I would encourage you to meet up with this therapist, even if you decide that just you and your husband (or you yourself) go first to vet her out. Bring up the issue of religion pretty directly if you think it will be an issue. It may be that she'll be a terrific match and has great skills and intuition, or it may be that it isn't the case and then you haven't dragged the kids in to seeing someone that you won't be continuing a therapeutic relationship with.
Good luck to you and yours.:)