Maybe sexual assault was the motive to visit her, and she fought back, and it turned into a murder. Then, the killer knew they were in trouble, and tried to clean up the scene.
Yes, that's possible. Since in this case there was no reason to hide the crime scene, her murderer must have been trying to disguise his own identity - although he'd never been DNA tested or fingerprinted in the past. Perhaps he also tried to disguise shoe prints or other evidence criminals don't usually think about.
I'm sure there's many details police are holding back.
In terms of lunatic killers vs methodical ones, I'm afraid cases like Russell Williams have convinced me you can't always make thise distinctions. He broke into over 80 homes, before assaulting a couple of women in their homes, and then murdering two others in their homes. He'd was caught because of the distinctive tire tracks left in the snow by his car. Hopefully he is a very rare type of killer, but I think police are now aware of such possibilities and keep them in mind, even if it was not the case here.