I agree this sounds like a poorly conceived hunch - I'm kind of shocked a profiler would publish it - especially considering the potential impact his theory would have on the daughter.In the book PB only gives a summary of what he suspects happened. I don't think he has solid evidence to back up some of his hunches, or he would explain more in the book.
He thinks the killer was watching the house, because the killer struck within minutes of Janet going to bed. Janet didn't ever draw the curtains or blinds, so anyone watching the house could have seen her go up the stairs.
We know Janet wanted to go early to bed, because that's what she told her daughter on the phone. But a killer wouldn't know that.
If someone went upstairs at 8:30 pm, in a home believed to contain a teenager, why would he assume both of them were sound asleep and it was safe to start cutting the glass?
JMO