If your mother is not in a hurry, she could look at sales...I know that JoAnn's has some nice quilt quality fabric on sale for 50% off. I also know that most local Quilt Stores have a section of fabrics on sale. I don't use sheets for backings because my machine does not like them....
You must also decide on a pattern that does not take too many fabrics because there is were sometimes it becomes difficult to match and arrange colors. Scrappy is sometimes the best.