Recognising unpleasant truths doesn't seem to be one of Mrs. Bennet's strong points, but it's hard to tell how much of her self-deception is unconscious. When he does or says anything that could be seen as positive (saying Bingley would like her best, or being secretive about his visit as a joke) she takes it at face value and goes along with him. But his more openly nasty comments she sometimes complains about and sometimes tries unsuccessfully to ignore.

Is it possible she realises how annoyed he can be with her? Since she's no match for him verbally or mentally, maybe pretending not to notice or show that she's hurt is her way of dealing with him. And she consoles herself by believing that his compliments are sincere.