It's a lovely quilt. Doing something with your sister sounds like like a good use of time. How about an applique BOM? That might be a good challenge and fun.
I agree on the triangles. It's like making the thing twice. First you cut it, then you sew it and then you have to go back and trim them up. If they would just work the first time you make them, it would be different. For me, they don't. I can't imagine how much time it would take to make a bed size quilt with a bunch of triangles.
It's like making a Disappearing nine patch. You make all your blocks and then you cut them up, square them up again and sew them back together. It's like making it twice. It's so much easier to just make it with sashing and strip piecing.
Maybe my quilting life is destined to be mostly I Spy quilts.
bkay