With all due respect, those of us not at the scene are not in a position to know where the tape should have been. Those on scene make that decision based on what evidence they think they need to process. As I said, IF the body was wholly in the culvert/creek, on the west side, there is no need to tape off the scene unless there is evidence to process or any need to work there, without interruption.
There's no minute inspection of every blade of grass. Obvious evidence is obvious. One reason might be to close an area off to search for shell casings (not in this case). But once the body is removed from the water, if there is no indication she went in that side, and no evidence to process, then there's no need for the tape.
It is certainly not automatic that the area around a body is taped off. It depends on how access needs to be controlled and what is going to be done there. And what visible evidence/clues there are.
I've worked MANY death scenes where we didn't put tape up.
And we rarely put tape up overnight. You get in, process/search the scene, and get out. Leaving tape up overnight would be pointless unless staffed by police/SAR to keep people out. I do recall one scene we did leave a deputy overnight, with tape, because we couldn't start the scene search until early the next morning.