I've used this Retayne/Synthropol combo successfully on fabrics and clothing that bled (
https://www.dharmatrading.com/chemicals/retayne.html), but that was on something that was all one color, so it wasn't a problem fixing any loose dye with the Retayne, because it was fixed to something the same color.
Since your quilt is all put together (and therefore NOT all one color), I think you might want to just use the Synthropol.