Gertrude has a very minor role here. She is Hamlet's mother, who has married his uncle after her husband was killed. She seems totally oblivious to what's going on, and does not even understand why Hamlet is upset. It's significant that Alfred, wearing a dress, is mistaken for the queen. She is much more of a figure than a character, having little more significance on the stage than an ordinary prop (either because she is thinly drawn or because she is so clueless).