Bless you for your kindness, this will be so special to your aunt. When I have made memory quilts using knits it has been easier for me to handle if I press a light weight fusible interfacing to the back if the fabric before cutting to the size/shape I plan on using. One quilt with mixed fabrics I made disappearing nine patch. The woven fabric around the knit helped keep everything smooth and straight. Have you thought about using a carpenters for the center block then working around that to get the size you want?