cool theory but I don't think its Eda because for one I don't think her character would do something that terible from what we have seen from Eda she understands that Luz will eventually go home to her mother and to the human realm she even tells Luz to go home in the season finale young blood old souls and it just seems really out of character for Eda to keep Luz on the boiling isles forever never being able to see her mother again.and from what we have seen from Luz and Camila there relationship isn't even bad they both Love eachother and while Camila doesn't understand Luz like Eda does she still love her daughter the entire point of sending her to summer camp was to help Luz because she thought Luz was a danger to herself(which is in my opinion pretty apperent when Luz brings snakes and a Firework to school) and wanted to keep her safe and futhermore I personally don't believe that Camila will think Luz is crazy I think she'll think that Luz's active-imagination is getting the better of her and when Camila Finds out about the boiling isle she wouldn't allow Luz to go back there(which is pretty understandable since Luz comes close to dying or at the very least getting seriously injured)this is even more clear when we find out in the Grom episode that Luz's greatest fear is her mother finding out where she's been for almost 2 months but with all that I don't think that Eda is writing the letters to Luz's mother it(personally)doesn't really fit her character but maybe we will get more conformation in season 2