There’s nothing wrong with having a happy life.
幸い is listed as a noun and na-adjective meaning happiness, luck, fortune. As an adverb it means luckily, fortunately.
So in the context sentence I’m confused about 幸い being right before 命 and resulting in the translation “happy life”. As a noun shouldn’t it be 幸いの命? Or as a na-adjective shouldn’t it be 幸いな命? And I don’t see how it could be modifying the noun 命 as an adverb given the meaning of 命 (if you can even use adverbs to modify nouns in Japanese; I have no idea).
What am I missing?