I never heard of folding on bias. Sorry but I do not think I could do it if I wanted too... I do re-fold with different crease lines. I store my quilts in the closet with all my other blankets and sheets. I use my quilts but I have Grandma quilts in a glass case.
I wonder if she let's her kids sleep under quilts. I made my kids quilts for spreads and they still have them after 20 years of boys folding, dragging and craming quilts. Still look pretty good.