Once the defendants sister had shot all the occupants in the house there is nothing to prevent her from using either the kitchen sink or the bathroom sinks. After all that is what sinks are predominately used for is it not? 
So you are suggesting that the blood stains are not associated with the wounds to Sheila?
I won't agree or disagree with that, but you must then be of the opinion that when Sheilas body was found, her palms and fingers were clean and not contaminated with blood, right? Like the pathologist and police officers witness and testify?