Hat Game

Beth, Anne, and Susan are the three finalists in a logic competition. A final test will now be given to decide the winner. The three girls are sitting together at a round table and are blindfolded. The moderator informs them that he will either put a red or green hat on each girl's head. Once he instructs them to remove the blindfold, they must raise their hand immediately if they see a red hat. Based on who raised their hand and what color hats they see, the first girl who can determine the color of her own hat will win.

The game then begins and the moderator decides to put a red hat on each girl's head and informs them they can remove their blindfold. All three girls immediately raise their hand (as each of them sees at least one red hat). After a long pause, Susan tells the moderator that her hat is red and explains why. Her logic is correct and she wins. How did she do it?