I am an atheist, my sister just died, I grew up in a place with almost no Jews and don’t really know how to sit shiva…

I am not a religious person, but my family is Jewish, and my sister will be buried on the Jewish cemetery tomorrow. I visited people who were sitting Shiva only once before, since our Jewish community is tiny. Now, my sister died, and I would really like to sit some form of Shiva. I do not think I can obey all the rules. I was wondering how non-religious people go about it.