What is Fanny's message in paragraph 6 of Progress Report 12, April 30th in Flowers for Algernon?
The paragraph you mention talks about Charlie's nightmare, and in my copy (Bantam 1996 Edition) is dated June 5th. The only reference to Fanny I can find is an indirect one, where Charlie describes the bride and groom on the wedding cake pointing at him and laughing. A connection can be made between this image and Fanny's conversation with Charlie in Progress Report 11, May 20th.
In this conversation, Fanny, who is the only bakery employee who didn't think Charlie should be forced to leave, is staring down at the bride and groom on the wedding cake she is decorating as she speaks. Fanny thinks there is definitely "something mighty strange" about the way Charlie has changed, and she wonders if he has done something evil "to get (himself) so smart all of a sudden". She refers to the Bible, and likens Charlie's transformation to eating from the tree of knowledge in the Garden of Eden, and tells him, "if you done anything you wasn't supposed to...like with the devil or something - maybe it ain't too late to get out of it...maybe you could go back to being the good simple man you was before".
Fanny's distorted message as it appears in Charlie's nightmare through the bride and groom on the wedding cake is that, like Adam and Eve, Charlie has done something forbidden and possibly evil in turning to science to increase his intelligence. To Fanny, Charlie has become a kind of freak of nature.