I agree that it will be a lot of work, and the key question is -- to what end? Is the desire to make it usable again? If so, I think it's not realistic. Even if you applique new fabrics over the most frayed, other portions of the quilt will start to fall apart.
If it's to just stabilize what is, and accept that it's heavily damaged, then i think the bridal tulle technique is the best option. If the hope is to have a keepsake of this relative, I think what I would do would be to photograph the quilt, individual blocks and the entire thing. Then I would stabilize with tulle and all over quilting. then I would cut portions that are in fairly good shape and make wall hangings, pillows, table toppers, or other items that would not take a lot of abuse, and I would make the salvaged portions up into those keepsake items. They would make nice gifts for family members who remember her, along with a collection of photos of the original quilt.