Carrie’s had a lot of problems since she became Stalker.
Nights of little sleep, trouble keeping her grades up, no social life, worries about protecting her secrets, job and family getting in the way of her “recreational” time.
Now, confronted by Eric and his problems, she comes to realize where the problem really lies. She made the choices that brought her these problems, and she can undo them just as easily by making a different choice. At any time, she can just walk away from it all, lay down the mask and go back to her privileged, normal life. Some people don’t have that luxury.