I do not recommend that you place decorative items in your tank for a simple reason: They can be dangerous for your tarantula if it should fall on top of one, such as the typical cactus plat, or a sharp stone.

Another reason is that it would make it harder for her to find and hunt her prey. This would cause your tarantula to go hungry, and the prey to wander around in search of food. The prey could become the hunter if it decides to bite your tarantula if it is molting and defenseless. Remember that this is the moment when your tarantula is most vulnerable.