If Arias had left Travis where he was, he would have been right by the bedroom door, with is roomates' bedroom doors not too far away, making it far more likely that someone would notice a smell of decomposition. The time it took to move him was worth it, to avoid that. (I've also often wondered if there was an extractor fan in the bathroom, turned on.)
Also, it wouldn't have taken much time at all, or required much strength. The total distance was about 14', covered with tile and slippery blood, and of course Travis' body was slippery too, being naked and also covered with blood. To make it easier yet, he was already lying along more than a third of that distance, so she only had to pull him about one-and-a-half times his body length.
Then, for cleaning herself, there was the bathtub right next to the shower. I don't recall any mention of it at trial, but it's certainly the cleanest object in the bathroom. However, I do recall evidence that she'd tried to clean Travis in some way - quite possibly she showered standing over him, or before putting him in the shower.