Luche had absolute confidence in her strength; she knew that most people would never be able to bypass her and reach the golden nail as long as she was there.
In the game, you can't walk out of bounds and enter the temple from the opposite direction to directly bypass the boss area.
It's possible to do such a thing in reality, but Luche is not a mindless boss like in the game; she can easily sense your presence from kilometers away with her pseudo grade-0 capabilities.
If not for the suppression of miasma, she would have already ascended to grade-0 right after Zion.
The main reason why she just put some random stones to hide the path to the golden nail was also her confidence in herself that no one would be able to reach it unless they defeated her.
Zion likely told Luche about the importance of these golden nails, and even though she's a maniac and has a very unstable personality, she's not someone who wants the world to get destroyed either.
