As the first on the scene, Natalia should have made sure there was a clear path to the body, or cleared one for CSI's and ME to get to and from the body, but she did no such thing.
When Calleigh is talking with Alexx at the elevator crime scene, she pushes the metallic evidence collection box previously placed on the floor with her foot. This has the potential to cause scratching on the floor which may be misconstrued as evidence during collection. This is not something a trained CSI officer would do.