Once inside Diaanja's Retreat, you have to defeat five Servants of the Harbingers of Death and one Harbinger of Death.
You should be able to make quick work of them. Continue on and you will come to Diaanja.
She greets you by setting her "dog" on you. The "dog" in this case is Diaanja's Bodyguard.
After defeating her creature, talk to Diaanja again, and you will find her attitude has changed. (Whatever she has to tell herself to be able to sleep at night...)
At this point, the unexpected happens, Mishirla turns on you.
Do what must be be done. Then talk to Diaanja again.
Finally search the chest and this quest is complete.
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