The timeline in this case has me absolutely convinced this was someone who knew or had been watching Holly.
Nobody gets that lucky with time. Managing to strike in the short minutes early morning between her dropping son off and answering mom's daily call? No way.
I would submit that the moved table, spilled coffee and glasses on the floor might have occurred when the perp grabbed her by an arm and gave her a pull. The lack of yelling or fighting may indicate she knew here abductor.
Perp gets in either by deception or stealth, confronts Holly, grabs here by the arm, a small struggle ensures as she tries to pull away, perp brandishes a knife or gun and Holly gives in. Perp takes her out the back door to reduce the chances of someone seeing her being abducted.
At least this is what makes the most sense to me.
And neighbours noticed the back door was open. So I presume they were in when Holly disappeared, but didn't hear anything suspicious, or see any strange vehicles?
It would be good to tighten up the timeline here - the time Holly left her home, the time she dropped her son off, estimated time she returned, time the last person saw her, time her mom called and time her mom arrived at the home. The time neighbours spotted the door open would be helpful too.
Just jumping in quick----was the coffee cup on the coffee table? Or had it spilled in kitchen, on counter top and / or floor? Was milk or creamer on counter? Spoon in sink? Coffee maker still on? How full was the pot? And was her lunch made for work? I think this can give us clues on where Holly was at in her daily routine.
OK--back to reading!!!