Regardless, since I knew, I wanted to at least give her a condolence card. But writing condolence cards in one's own language with some understanding of cultural precedence is hard enough. How to go about it in Japan, but from a foreigner, seemed quite difficult. I managed to get enough information from the internet to write the basic phrase used to express condolence: okuyami moushi agemasu. But after that, it was hard to know how to really phrase something so that it didn't sound really clunky, or at the very worst, offensive. So I simply wrote in English as clearly as possible, hoping that the vague meaning of it would trickle through.
When I arrived today for my lesson, she seemed unchanged, greeting me warmly as usual, running off to the kitchen to get the tea and snack that she always serves. When she came back I said, "Okaasan," mother, to let her know that I'd heard and was sorry. And she continued as though I were a child, explaining the existence of death to me for the first time, trying to soften it and make it seem less scary. Her mother was 87 years old, and the gods had looked after her for a long time and now she would be going to heaven. And then she told me about the ways to say that someone has passed away, taught me how to offer condolences in Japanese. It was a lesson like any other. She said she thought her mother was happy, and so Fukunari-sensei said it was ok, though she did admit she was a little sad.
And knowing Fukunari-sensei as I know her, I believe that her mother was likely a happy person and had a good life. I'm happy to have Fukunari-sensei in my life and grateful to her mother and her mother's memory.