The Death of Flemeth?
Flemeth saved you during the first stages of the Blight, and her daughter Morrigan helped nurse you and Alistair back to health. Morrigan later revealed that Flemeth was an abomination who has sacrified her daughters to preserve her own unnatural life.
You agreed to confront Flemeth before she could sacrifice Morrigan and found the enigmatic old crone at her hut in the Wilds. After a short exchange, she shapeshifted into a high dragon, and with difficulty, you killed her.
So much about Flemeth remains a mystery. Standing in front of her deserted home in the marsh sent a shiver up your spine--like someone walking over a grave.
Related codex entries
This codex entry may only appear if the Warden has killed Flemeth during "Flemeth's Real Grimoire", Morrigan's personal quest.