It never got to the point where she had to stop questioning if was Damon or not. This could either be me thinking to much into it or not but I think this is because she didn’t believe that Damon had come to be her knight in shining armour she had to reassure herself that it wasn’t a crazy fantasy
"Katherine: The brother who loved me too much and the brother who didn't love me enough. Damon: And the evil slut vampire who only loved herself." In all seriousness though, is Damon really in a position to be calling other people sluts?