You'll receive a few messages in combat as Alsha loses HP. Once she is reduced to around 20%, the message will show up that "Large drops of oil begin pouring from the eyes on the mannequin" (this is the third message), and Alsha will repeatedly cast Fire II on herself until she dies.
You or anyone in your party must deal the final blow to defeat her; if she kills herself, you will have to rezone and try to kill her again.
Once Alsha is defeated, each member of your party can select the ??? again for a cutscene in which they obtain the Better Humes and Mannequins and complete the quest.
Once the quest is completed, Fyi Chalmwoh will change the pose of any mannequin you own as often as you'd like, for 200 gil each time.
Enaremand (Third floor, Tavnazian Safehold)
Eneremand's final masterpiece is complete, but not as complete as he would like. The troubled mannequin craftsman has now asked you to help him find a necromancer in order to breathe life into his creation...
SPOILER WARNING: Click here for additional details about this story line.