Sorry... it's been quite some time since I've last played this game... but if nothing has changed since then... After you get the moth dust and talk to the blood fey to trigger the event...
"There will be a room on the left of the cave where you find Shayla that you can (insert it into the nest...) it's before the boss room. Do not enter where Shayla is until you've poisoned the nest with it. Then kill all the bugs that come out of her if I remember correctly..."
Sorry... tried to state all the details at the time of writing that quite a while ago... my b. Hope you get it figured out. Feel free to post some screen shots and advice or corrections to help others who have the same issue. I'm sure it will help everyone that plays this great game in the long run...
When I get back around to it I'll have to correct any mistakes I made if I go through that part of the game again... but don't hold me up to it or rely on it lol... it might be quite some time... I've kinda fallen out of game since then for the time being... This is still on my to support list though.
Anyway, hope this helps... Have fun! ^_^