Looking at your otp like
Mrs. D is the one with a twin. Her twin is the fragile patient from Radley who killed Toby’s mom. That’s why she was on the board there. The twin escape That Night and tried to kill Ali. That’s why she hinted at seeing Ali die, yet hasn’t spoken up. To protect her twin. Cece is the daughter of this twin (Mrs. D’s niece and Ali’s cousin) so if she AND Mrs. D saw this happen and thought Ali was dead, they would protect the killer. Mrs. D is probably just trying to pin it on spencer.