There is a letter from the Shadow Druids to Kagha, it takes a perception check to find it. I think it's bugged and doesn't open up new dialogue choices however.
Worked for me - granted I did first pick up letters in Kagha's quarters first. And the sent the letter from the tree to camp - not sure if that changed anything.
Also prepare to have nightmares if you decide to confront Kagha... Wildshaping druid in a cutscene can bug out.
