I haven't once seen anything about your love for her, or lack of it. It sounds like you have been feeling stuck with a clingy, needy lady. Chances are, if you got married, she'll be clingier and needier. That leads to suspicions and clandestine snooping. You are already feeling smothered. I can only imagine what's around the corner.
Regarding her saying that she feels this is God ordained, I highly doubt it. If it were, you would want the marriage as much as her. Unfortunately, it is most likely her ascribing to God her own desire (which is very common), or in the worst case, manipulation to get you to marry her.
It also sounds like you are looking for advice on how to break it off without upsetting her. You can't. No matter what words or tones you use, she will be devastated. But what would devastate her more is if you chickened out of your plan and married her. Imagine how she'll feel when she realizes that she's in a loveless marriage and that you are always trying to get away from her to breathe. Or worse, if you allow her to talk you into having children, even though you don't want any. Eventually, she'd most likely wind up a struggling single mother, as we have all seen so many times.
I realize these are worst case scenarios, but it sounds to me that if you don't follow through with your plan to break up, they are all very likely. So if you really need to do it, then do it quickly. Don't cave and allow her to talk you into repeating the same pattern over again. Be strong and gentle. But if you're looking for an easy way to do it, you won't find any. Let her find someone who appreciates her ways. It's obviously not you, so let her go so she can find happiness with someone who really loves her.