Kilandra, from Ultima VIII
Kilandra is a poor fisherwoman on Pagan who seemingly has gone mad.
Prior to Ultima VIII, Kilandra's daughter had become sick. Since no Theurgists were available, she tried to plead with Mordea, who also had healing powers, to help her. However, Salkind told her that Mordea's bath was more important than this and Kilandra's daughter died. She seemingly went mad over this, saying she talked to the fishes.
Some time later, the Avatar was on an quest involving a strange ghost armour. After going receiving hints from Orlock, Corinth and Gwillim, the Avatar found a cave in Herdsman's Valley, but the doors were locked. So the Avatar followed Gwillim's clues and visited Kilandra at Fishermen's Reef. Kilandra spoke about her sad story, and the Avatar had to be compassionate before speaking about the ghost story, then the cave. It turned out that the ghost of her dead daughter had the key.
So the Avatar visited the Cemetery and the ghost released the key when the right grave was visited.