The Fair Lady, sister of Quelaag and leader of the Chaos Servant Covenant appears to be a mute when you talk to her. All that changes once you wear the Old Witch's Ring.
The Ring appears to have no other use. It simply allows for more story to be told.
You can select the ring as one of the Starting Gifts or by trading a Sunlight Maggot with Snuggly the Crow.