You need to find the last of the first 4 clues. The one you're missing involves something she talked about at Lighthouse of Selsey. It's also possible that you said the right thing already but because of a timing issue (the auto-chat feature, for instance) she didn't "hear" what you said so just be persistent about it and it should trigger her memory. If for some reason it still doesn't work, let me know your username and I'll check your log. Thanks!
Viewing post in Cheree: Remembering My Murder jam comments
I'll note that I let myself get bogged down in the Lighthouse, too, as I figured it was important, but then I followed a blind trail for the conversation.
But then I astravel'd away and back again, and Cheree's opening dialogue pushed me where I needed to go. This helped somewhere else, too, (where isn't important--just the general mechanic to refocus myself) though for all the other clues, I didn't need it.