If the fabric is 45 inches wide, you are short of fabric width by 23 inches (that would be 6 inches header on either side. The 85 inch length is about right (40inches X2 plus the 5" makes 85 inches). The quilt is 77 long and adding the 8 inches makes 85 which is shorter than what you would like to have. So essentially, for the width, she needs another half width of fabric. So, another 3/4 yard of fabric split in the center and stitched together end to end would add the necessary width. But, the question is whether or not so many seams on the back is acceptable. Another question to be considered is the intended binding. Of course, there are other alternatives-a pieced section made from blocks or strips from the front. I like pieced backs, but I know that is a personal thing.