There is a section that discusses Bengali tradition here but Kali's presence in the story could mean several things...

...en.wikipedia.org/wiki/Ka...

I think the whole idea of Kali being the Hindu goddess of time and change could fit since toward the end...

...time and change (over several weeks and weather changes) cause Miranda and Dev to drift apart.

woah. I just thought that it was a scary picture to Miranda

I think it was that the culture frightened her before, and then, as an adult, she saw it in a new light.