Reading Tom's message here, especially the line, "If he did stir up Lucy's suspicions, perhaps all he did was to say Elinor's name once, with a hint of a reverent tone in his voice" stirred up some agreement in me.

Since we mostly agree that Lucy has lied, several times, in fact, it seems likely that she is also a suspicious person. So, as Tom said, I'm thinking that just about any little tidbit that Edward dropped about Elinor within Lucy's hearing would cause Lucy to build up the whole story in her mind about his regard for Elinor. I have been uncomfortable all along with the notion that Edward spoke to Lucy, in ANY manner, about Elinor, so this idea makes a lot of sense to me; thanks Tom!