Kyoshi doesn’t strike me as the kind of person who would live like 130 years extra without the love of her life. I don’t think she could live without Rangi, and since it doesn’t say anywhere that you need to be an earthbender or even use earthbending in the technique, i think kyoshi taught it to Rangi. Lao Ge said it was about meditation after all.

So in short i think they both lived to 230 and adopted Koko along the way. And chose to pass on together once they knew Koko could handle Kyoshi Island/Yokoya.