If Leonard is more an intellectual idea than a real character, we might say that Mrs. Wilcox is more of a spiritual concept than a person. There's something otherworldly about her from the very first moment – when she notices somehow that Helen and Paul are "in love" – that continues to linger in the book in a loving fashion even after she dies. The other characters, namely Margaret, also notice this. Margaret and the narrator both comment consistently about the spectral presence of Mrs. Wilcox, who haunts the story and the house (Howards End) like a friendly ghost. She always seems to be around at key moments, like when Margaret's deciding to marry Henry, and somehow, we get the feeling that she's involved in the decisions made.
Creepy, right? We're not sure exactly what the deal is with Mrs. Wilcox and the strange, gentle, but urgent power she seems to exert, especially over Margaret. In fact, Margaret is more and more possessed by an odd kind of Mrs. Wilcox-iness over the course of the novel. Of course, she legally becomes the new Mrs. Wilcox when she marries Henry, but her transformation is more than just a name change; she takes on the same kind of grace and wisdom that her predecessor had. Miss Avery, Mrs. Wilcox's old friend, makes it clear in her eerie way that Margaret is the new Mrs. Wilcox in both name and spirit.
But what do we know about the original Mrs. Wilcox? The answer is simple: very little. She's always presented at a kind of distance from us, as though we can't really know her; we only get snippets of her personal history, and we barely get to see her at all before she dies. Really, we rely upon the memories and musings of the other characters as they process her death and her continuing influence.