http://purlbee.squarespace.com/sunny-tied-quilt/ was the site listed in her earlier post. The biggest design element is that it looks like two strip quilts side by side. To say you want to adjust that design element out of it, why not just choose a different pattern, rather than re-invent the wheel?
Unless your sister has a 40" wide bed, it will come out in sections.
I think you might be happier trying a beginner pattern with no math and substitutions. Have you looked at ShellyQ's tutorials? She has several that make quick and easy quilts.