For those who say you can't find anything in the Rule book, 8.1c says, "If a player improves the conditions affecting the stroke by moving, bending or breaking an object in bread of Rule 8.1a(1) ... There is no penalty if, before making the next stroke, the player eliminates the improvement by restoring the original conditions..."
While the Rule says "the player eliminates the improvement" this doesn't mean the player must take an action to remove, merely that it gets eliminated.
For example, a player goes under a tree and moves a branch out of the way in breach of Rule 8.1a. The player then decides to get another club and steps out from under the tree. The branch, on its own, goes back to where the improvement is eliminated. The player then goes back under the tree, but without moving the branch this time. There is no penalty because there is no improvement. This is essentially what Lexi did. She moved the grass, it moved back on its own. No improvement, no penalty.