Sarah FROST??

And frost is ice. And ice means diamonds!

... and also, a freezer - being the opposite of a defroster - could theoretically be called a froster ... which played a significant role at the very ending (Sarah not behaving like the usual oh-so-honest characters in similar situations and scenes of other movies was a relief for me, making up for some pesky other things that happened before).

Please do not spoil when answering.