Why at the house?
From the beginning, there was talk that it wouldn't be a hit-man because a hit-man would just shoot the victim and leave. "Shoot and leave" didn't make sense to me, because if it was a hit, they wouldn't want it to look like one, so it would at least need to look like a robbery, or in this case, a possible robbery gone bad, or a random lunatic.
However, if it was a hit, why wouldn't they do it somewhere else and make it look like a purse-snatching gone bad, for example? Seems like that could be staged a lot easier and would leave much less forensic evidence. If they knew her movements, they could have waited for her in any parking lot with a ski mask, grabbed her purse, and shot her whether or not she struggled.
Just odd to me that they potentially spent hours at the house, and took the chance of being seen by neighbors, etc. Which makes me wonder if there was something in the house they wanted.