I am always amazed by how colors can "change" dramatically according to what fabric you put next to it. I think you can tone down that bright yellow if you find a different sashing fabric. If it were mine and I had nothing suitable in my stash, I'd take a block with me to the fabric store and see if I could find something that would make the yellow more subdued while miraculously showing off the bonnets to their best advantage at the same time.
Sometimes a quilt block looks great all by itself, but a whole quilt of the same block is sometimes overwhelming. I like your Sue block and think she's well worth saving.