@Borderline
Remember than Mia has been physically abused by Sara from day 1 and also under the brainwashing effect.
Kinda think about it.. The doll influenced the shadow. So mia's shadows abusing her might be her own doing. Maybe she has some machosist thing going on. Anyway I can see the betrayal coming soon from her.
Man I hope Mia's personality isn't being too warped by Sarah
You're forgetting that was after a scene were Mia returned to her room and found the doll Emilyko made for her broken and sooty handprints covering every inch of the room. It's pretty strongly implied that it was Sara's doing.As andriod16 said, the shadows are influenced by the dolls, not the other way around. The dolls' personalities are reflected in the shadows. Kate is an exception to this, and now John to an extent.
If you remember, in the chapter where we see Sara beating Mia, Mia specifically asked her to do so. It wasn't a punishment or for fun, Mia brought a lash or whatever to Sara and said something like "Please help me do better as a living doll". Or something along those lines. Sara responded "Very well" and only then did she begin hitting her.