Glass
One thing I noticed during this movie was how many things were seen through or reflected in glass. The rich man's house up on the hill is seen through windows,the view of the city form the same house, reflections of characters in storefronts, and especially the confrontation at the end in the prison where you can see the characters and their reflections as they view each other through glass. There are many other examples, too.
She just goes a little mad sometimes. We all go a little mad sometimes. Haven't you?