Obviously I can only tell you what I would do in that situation. Since this is a grad. gift quilt and therefore, time is of consequence, I would set aside your "error" and make something else for her. Later on, after the gift is completed and given to the graduate, come back to your log cabin. Again, I can only tell you that time works FOR me ... when I am stuck for an idea or a plan of action, I do nothing ... and, in time, the solution to my problem pops into my head or I get an idea from another source, or I've gotten over my frustration and I can work on the troublesome one again without bringing on a stroke.
If you are very frustrated, I think it best to make this one a UFO temporarily.