So, I just did this encounter (Deyid was my last kill for the conqueror achievement, now I never have to go back to this stupid zone again), and it seems like the conversation with Seilaen can vary from what's in the writeup above. From my log, here's how mine went:
You say, 'Hail, Seilaen'
Seilaen looks at you with eyes wide with fear. 'Who... who are you? You... You must help me!
You say, 'I will help you'
Seilaen says, 'The forest, it... I can feel it looking at me... following me! Oh, I just want to leave and go!'
(At this point, I waited, but she never talked about having a locket that she couldn't make work, so, just to see if I could nudge things on...
You say, 'what locket of escape'
Seilaen says, 'My mother always carried this with her. I have no idea why I suddenly have it. Perhaps I can make it work for you, if you want me to?'
You say, 'I want you to'
Seilaen says, 'Oh it worked! Are you still here? Oh, please, don't have left me. Come tell me you are still here!'
(At this point, I'm ported to the top of the plateau as expected)
You say, 'I see deyid'
(No big monologue from her about how it must be Deyid causing all the trouble)
Auto attack is on.
Deyid the Twisted issues a deep rumbling laugh as his branches descend to club the life from you.
(Deyid gets the smackdown)
An eerie silence settles onto the forest as Deyid the Twisted slumps over, defeated.
You have slain Deyid the Twisted!
Seilaen shouts, 'Oh, thank you! Thank you! I don't feel the trees watching me anymore! And... Let me try Mother's Locket again, I think it might work...'