The Palmer House - a portal?
100% agreed and even further, you will note that no one EVER removes that picture and...
Sarah is now inhabited by Judy/Experiment.
This could have happened at any point from then on, or she always was (bug in mouth during season 8)
The portal has been there since the picture from Tremond/Chalfont...Based on current and past owners of the house this is how things have transpired.