1. She buried the shovel in the sand = she made a hole and put the shovel in it.
2. She left the shovel buried in the sand = somebody made a hole and put the shovel in it; she walked away and left it there.
The first is an active construction where she had actually done something to the shovel, but it doesn't mention her leaving/departing the scene.
The second is a passive construction where something is being done to the shovel by her, and it does mention her leaving the scene and abandoning the shovel, so there is quite a difference in detail between the two.
We don't know that she did anything with the shovel. I think in the right context the sentence would be true even if she didn't know about the shovel.
She did not dig it up (perhaps because she didn't know it was there) and she left.