In the context of her possible alliance with Graendal that all her allies died (i.e. were actually killed by her), when they lost their usefulness,. This foreshadowing might not fit 100 %, namely that Aran'gar directly or indirectly killed Graendal, but I would say most foreshadowings aren't 100 % accurate.

However, the quote still fits in an ironic way, namely that the author made Aran'gar's cynical thought actually come true: Aran'gar's new ally Graendal died lile every of her allies before at a time when she wasn't useful anymore in Arad Doman and in the story, misfortune actually played a part in it, and there isn't even a grave because of the balefire.