Wool for sure would be the best choice. 2nd choice would be QD Request but that will show little to no definition in your quilting. Or cotton flannel. Whatever you choose, make sure it doesn't include synthetic fibers like polyester, rayon or "bamboo" (the stuff marketed as "bamboo" is actually a type of rayon) as those fibers don't breathe & trap in sweat and body heat. Wool is fantastic -- warm in the winter, cool in the summer. It wicks away moisture so you are comfortable regardless of heat or humidity.
Also, you could pick cotton fabrics that are less dense (like 1930's & civil war repros and some others). Less dense fabrics breathe more & keep you cooler. Definitely wouldn't use bed sheets for the back if her goal is to keep cool. It also helps not to "overquilt" (tiny, dense fillers) and to use 100% cotton thread if you plan to quilt less than 2" apart.
Last edited by Bree123; 03-15-2016 at 01:49 PM.