Spencer has an unknown twin. She is AD.We know Spencer was born in Radley to Mary Drake. Mary Drake is a twin so having twins is very likely. In the episode where Hanna is trapped in a room by AD,she had a”dream” that Spencer comes to see her. In this”dream”, Hanna says that she thinks this A is smarter than the others. Then Spencer says, “you told them the truth right?” Why would she ask that? Then Hanna says if she knew who killed Charlette she would tell A. That’s when Spencer tells her that if there’s a way in,there’s a way out. After she wakes up,she gets out. That’s because Spencer’s twin let her out after she found out that Hanna didn’t kill Charlette.And of course she would be angry at whoever killed her because that was her sister. And I’m sure Spencer’s twin would be extremely smart because Spencer is and so was Charlette.