This will be a gorgeous quilt. If you are making HST's you add 7/8 to the size to get the finished size HST you want.
Example: 5" finished (5&1/2 with seam allowance) add 7/8 = 5&7/8
Two 5&7/8 squares, right sides together, draw diagonal down middle and sew 1/4" on each side, cut on drawn line and you have two HST's 5" finished size.
Cutting 8&3/8, subtract 7/8, finished block is 7&1/2. If you are consistant with all of the squares being 7&1/2 finished (7&3/4 with seam allowance you will be OK).
You may e-mail her to let her know this is a beginner pattern and it would be easier if you knew the finished block size.
I have quilted for years and I still want to know the finished size.