On the other hand what qualities of Hester seem to be diminishing during these years of wearing the Scarlet Letter? What causes these changes?

Hester's appearance has changed over the years, but for the worse. Rather than having her youthful good looks, she now seems more like a shell of a human being. Her "rich and luxuriant" hair either has been cut off or remains hidden under a cap. But she "might at any moment become a woman again, if there were only the magic touch to effect the transfiguration."