This has been talked about in so many ways, in so many places, and it's sometimes a big issue for people who convert, usually the idea that they won't be saying kaddish for a parent or sibling like they would if that person was Jewish.
But thinking about what Yerachmiel did for Nanny yesterday - she would have loved it. Psalm 23 has real Jewish authenticity, maybe even more so than Kaddish, which isn't even in lashon hakodesh.
And I think it had meaning for everyone else there as well. They're not Jewish, most wouldn't even know what Kaddish is... all they see is this boy standing up, pouring his heart out, singing something from the Bible that speaks of her life and her journey. That's got to be just as meaningful, and like I said, maybe more so.
This is actually a tremendously comforting thought, since I seem to have accumulated so many non-Jews in my extended family. There are real, authentic Jewish ways to remember someone... even if you're not saying Kaddish.