I too think I would pass on making the leotards into a quilt. I'd suggest that she makes a rag rug out of the leotards. I don't think the stretch would cause any problems with 'a rug'.
I've tried making things that were experimental--and can only say that they just don't turn out as well as using the right materials. Also they seem to be tossed because they don't work as well. Why spend all the time and energy it takes to make a quilt into some thing you don't think will work well in the beginning?