How was this scaling effect done?
My first assumption would have been green screen, but it's clearly not - she's taking on all the light and shadow from the scene around her. Even modern green screen probably doesn't look that good. Well maybe only nowadays, but certainly not back in 1972 or even 10 years ago.
She scales up perfectly, and then at the end, falls against the wall, interacting with the scenery.
You can even see her shadow interacting with the back wall on the left during the first half of the growing, and then in the latter half, her shadow is interacting with the fireplace on the left as well.
As far as I can tell, it looks perfectly real... and from a movie made in 1972.
I've tried to wrap my head around how they could have done it with forced perspective somehow, while moving her and the background towards/away from the camera, together or separately, but that just doesn't work...