Maybe I missed this somewhere but who else lives with her? Just her son some of the time? I highly doubt an 11 year old child would be the target. Or does she have a significant other? I suppose if she does, that person may have been the target.
It just seems like a really specific time for this assailant to be there. Many people don't arrive home at 530 in the morning from work. If this happened in the evening, I would be more inclined to think maybe this person even had the wrong house or something as a lot of people are arriving home in the evening. But 530 AM seems specific to her getting home from work.
I personally think she was the target, but that's just MOO and I could be wrong.