When I read what you said about Mrs Ferrars having no concept of honor her behavior toward Edward suddenly made sense to me. (As I was reading it I was thinking, “Have you met Edward? How could you think that would work?”)

It strikes me that this is another difference between Lucy and Edward’s family. His family not only tries to turn him into something he’s not but they can’t recognize his good qualities. Lucy may not be all that honorable herself but she does seem to recognize that in others. (For example she knows Elinor would be too honorable to betray a confidence and uses that against her.) If Lucy flatters Edward for good qualities his family doesn’t recognize he might feel she’s the first person to really understand him (or maybe the only person besides his father .)