Can't find ghost cow plant

MiataBearAre you playing with any mods (like BetterBuildBuy)? If so, please remove mods, delete the cache, and try again to see if it works.

Have you checked your Sim's personal inventory? I know that seems too obvious but sometimes it's the most obvious things that get overlooked.

NOTE: I don't have Life and Death, so I don't have any experience with the Ghost Cow Plant.

I had the same issue in my game. And, I saw the issue when I was watching a Twitch stream and the ghost cowplant did not show up in the household inventory after purchasing in the reward store.