Well, I am pretty sure I saw a picture of the crime scene of photos of the stairs with little blood drops, so I don't think it was completley clean.
But we see the swipes of blood on the walls, where you can clearly see that some bloody fabric was wiped against them. I am not sure exactly where those pictures are taken though. Just that a wall was smeared with blood.
You can wring out the towel so it's not dripping, but still wet enough with blood to make those marks. Plus eventually she put on his shower shoes, that were left just off the bloody carpet area, IMO. My feeling is that she kicked them off before heading back through the blood, and then slipped them back on when she walked out of it so not to track blood anywhere else.
Have they shown that blood was found in those shoes but not under them?
Think those pics are of the hallway leading to the bathroom. She left that blood in places probably on her way to dump the stuff in the washer.