Ahh, Crazy Quilts!!! I would use a muslin to foundation piece the blocks. Stretch velvets usually hold up to being pressed so you could try a fusible interfacing to stablize --- I don't think in the long run that I would use them. I would let her know that the stretch is permanent and might not do well in a traditional quilt like the crazy design. You can mix woven fabric types but to mix woven and stretch is asking for frustration at the very least. I am looking for the place that sells woven velvets --- think they are a JBMartin if I remember ---- velvet and a turkish towel for steaming or a needle board or velvet board --- do they even make them anymore? I really must check into doing some of my grandmother's style of quilts. Thanks for posting on the subject. Good luck with your adventure in velvets and brocades.