I feel for you. I am in a similar situation - albeit different in it's own unique way.
My wife has told me a few "little white lies" during the time she has been with her friend. One incident I can think of off-hand was where I asked her not to cyber with him while she was at home and I was at work (he lives 2 states away). When I IM'd her during work, she said things were "fine, nothing going on". A day or two later I asked her in person and she confessed she had cybered that night. Now, I know different situations, different transgressions, etc, but it was still her telling me a lie in the moment. I've since forgiven her, truly.
I guess I try to also see her point of view, and the "caught up in the moment" reason is probably the best I've heard. Their NRE is intense, and they find it difficult to control themselves, I can sympathize, but it also makes me jealous of what they have.
We are 99% honest and open with each other. I know we strive for 100%, but I have yet to see where that is truly possible.
Bottom line: You need to feel like you can trust her...like the times she might tell you a falsehood ARE few and far between (or never), or for the best interest at that time. (Honestly I would've been angry with her while at work, and her lying to me at that specific time might've been best as we could talk about it face-to-face later.)
I hope no one here flames me for having a slightly different take on this, but this is just my 2 cents.