The Red Woman takes her dress off and the amulet around her neck. And then she looks in the mirror to reveal: old face!
What's going on with that, you ask, because you are a person, and anyone who is a person is asking that? Well, for one, it would be inconsistent to say that removing the amulet caused her to morph into a saggy sorceress -- Melisandre has done that before and her pleasing Carice van Houton exterior has remained firmly (pun intended!) in place.
And it can't be that she's decided to give up and die. Can it?
Probably not. According to co-creator D.B. Weiss in the inside-the-episode extra posted above, this is all about Melisandre admitting the previously unthinkable to herself. "Her appearance is a lie, just as the Lord of Light's supposed promises and messages to her were lies," says Weiss. "At the end of episode 1, she's in a place where she needs to look her real self in the eye, and come to terms with where she stands now."