It is possible that she loves you and doesn't want to hurt you by telling you she doesn't want to be with you ever again.
I had that problem with my STBX. I didn't want to be with him but didn't want to hurt him, regardless of how bad he had hurt me. I wanted to work on things, even though I knew it was hopeless. I am hoping this isn't how your wife feels.
I am experiencing the same thing. I would add that things aren't always "black and white". When going through a huge decision like this there is always going to be doubt. One day she may be sure it's over and another day doubt that resolve. She probably isn't completely sure what she wants. The additional time apart may help her decide, or make it easier to leave without being wracked with doubt. But I agree - it's hard to hurt and let down someone you love and care about, even when you feel very strongly the marriage is not your destiny and it's the right thing to do.