The easiest would be a preprinted one that just needs to be quilted. Then there's one that's done on a cloth foundation, but that one wouldn't be easy for your mother to quilt, since there is an added layer of fabric, unless she wants a lighter weight quilt, without added batting.
The easiest one I've done calls for making strip sets and cutting them at an angle (the strip sets are off-set as well). I saw it in a class. I think it was called Lone star in a day, and it was pretty well done in a day. Another feature of this quilt is that it did'nt require y-seams. The corner pieces were sewn into each eighth of the star, and were stitched together when the eighths were stitched together. The eights were stitched together 2 at a time making a quarter of the center of the quitl, then the quarters were stitched together to form a half. Then the two halfs were stitched together. Then one finger in the center pressing down, and the points all twisted to make a perfect center without any bulk.
I'm with the other posters, that if a french curve is used, it's a giant dahlia, but I would have no idea how to use the french curve with that. If I did a giant dahlia, I think I would paper piece it in the curved strips going out from the center.