In the episode 'The Benders' when Kathleen is viewing the info on Sam and Dean, how doesn't he not realise that it's Dean.

Because at that point, Dean Winchester was dead. This was after the events in 'Skin' where the shapeshifter took on Dean's appearance and died. The police took that body and buried it as Dean Winchester so according to official record there was no doubt that Dean was dead until the Usual Suspects [they talk about St. Louis police exhuming the body they thought was Dean's].

The description that is given is very basic. Height, weight, hair and eye color. That's it and could match a lot of people. Not only that, Dean said that Sam was his cousin- so any resemblance could be attributed to the fact that he said he was related to Dean.

I thin that she was waiting for the right moment and then get him.