I think you are working from a very narrow definition of creativity. Your sister is clearly artistic and good at visualizing, but whether she's actually a creative thinker isn't apparent from your example. Creativity is regarded by many who study thinking to be the highest form of giftedness. That goes way beyond making a suggestion that improves a quilt design. You're giving your sister way too much credit and yourself too little. Some of the most creative people aren't artistic at all. And some people with artistic talent aren't particularly original thinkers.
hugs,
Charlotte