Come on, they had to make the prequel in line with what happened. You can't fault the Jedi anymore than faulting George Lucas. They had to do what they did for Episodes 4, 5 and 6 to happen. Case closed.

She's not Death per se, just another personification of Death like Hela. The Real Death would be an abstract entity which would be a concept not understandable by any mere mortal. Only god like entities like Thor can see these entities (like in Love and Thunder where he saw Eternity). Agatha and Billy, though powerful, are not god like entities.