I know this isn't likely, but sometimes I think the perp may have just been taking a chance. He obviously knew she lived there, but he may have just figured she would come out at some point in the morning but didn't know her exact schedule.
I got this idea from the HS case. Whether or not this is the same perp, it still gave me some ideas. HS's boyfriend was home at the time, and either the perp. didn't know or it wasn't enough to deter him, so either of the two of these could have been a possibility in Holly's case, too (with reference to the brother, this time). Another strange thing was that, from what I've read, HS had come out of the house and gone back in a couple minutes before her attack happened. I've always wondered why the perp. didn't do anything at that point. Asleep on the "job", maybe? Wasn't expecting her to come out so early? Wasn't paying attention? Caught off guard? Hiding out in the woods nearby and didn't have time to move in quickly enough? Regardless, he was obviously somewhere in the area and just waiting for his perfect opportunity, since she came out again a couple minutes later, from what I understand.
I guess my point is that the perp. in the HS case did enough homework to find out that a female would be coming out that morning, but I don't think he knew exactly when, and it's obvious that he didn't know or care if a boyfriend was home at the time. Like I said, whether or not it's the same perp., I don't think it had to be someone who knew Holly terribly well or was necessarily familiar with her routine beyond guessing that she'd be coming out at some point that morning. JMO.