I agree with washing it with Synthrapol and lots of color catchers. This combo should catch any remaining loose dye particles so they can't settle into other fabrics.
Next time wash a bleeder fabric like that in Retayne! Retayne permanently sets color. A few fabrics need 2 washings in Retayne. You never want to use Retayne on a finished quilt such as yours, though, as it will permanently set any unwanted bleeds into other fabrics. At this point your best choice is Synthrapol and *lots* of color catchers (I'd probably use an entire box!).