When Spencer sees Aria step out of her "room", pink streak in her hair and all, she feels relieved. And then she feels bile rising in her throat. She can't explain it, but she's never seen anything more disturbing than little Aria standing in the doorway with her butchered hair, quivering.
Emily joins them, arms crossed and not really meeting their eyes. Spencer hasn't seen her look this way since the time that Wilden outed her to the girls. Spencer wonders if Emily is upset about the kiss, or if…no. She can't let herself think that way.
Hanna walks out, the usual fire in her eyes gone. Spencer should be relieved that she, in fact, did not kill any of her best friends, but all she can think of is how miserable and broken they all are.
When Spencer tells the girls to set the dollhouse on fire, she knows that they could all burn to death. Part of her thinks that they would be better off. How could they possibly go on living their lives after this, like nothing ever happened? Like they would ever be able to forget. If they were dead, they would finally be free of Charles. Maybe that's the only way they can ever be sure of escaping him.
As she burns Charles' childhood memories, she feels a sense of peace. One way or another, the nightmare will end tonight. And if she dies? She never has to think of the What Ifs again.