Yeah, the sugar seems hard to avoid. I was thinking steamed spinach (SO GOOD in a Japanese restaurant, with sesame seeds and a soy-based glaze - not sure if there is sugar in it but it doesn't taste like it), seaweed salad, brown-rice sushi (hopefully they have it!). I guess you just have to ask about the sugar in all of the sauces...
I thought I remembered a thread about this topic but I couldn't find it. All I found was this thread from 2005
but it might contain some things to look for on the menu.
Good luck! And best wishes for your aunt.