I don't think Emma telling Harriet that Mr. Elton is "a social climber, self-centered and a snob" would have the desired effect. Harriet is a very young woman, barely entering life, and has just had her first dissapointment in love. I would think her reaction to such words from her friend, who persuaded her that she loved and was loved, would be more likely met with disbelief, anger and pain, perhaps to the extreme of disagreement, argument and a disassociation. No one, regardless of age wants to hear of a loved one's misbehavior. It takes time for those thoughts to sink in. I think Emma did what she could in trying to distract Harriet from thinking about Mr. Elton. Tha fact that Harriet found comparisons to him everywhere shows, to me at least, that she was not ready to listen to anything against him.