Well, while we've heard where the body was found, they were managing the scene, so I assume there was a reason to have crime scene tape on the east side and not the west.
If she was found in the water on the west side, and there was no evidence on the bank, and there were signs she entered on the east side, I could see putting tape there and not on the west. We only put the tape up to protect an area where we are working.
Or, the reports were wrong and maybe she was found inside the culvert itself?
Let me put it another way --- if we find a body in the middle of a river, we don't tape off the river edge, we tape off where we think we will find evidence, eg where they went into the water, where they died, etc.