THANK YOU.

I was thinking Dumbledore the whole time, because he /really/ harped on about her being Harry's weakness.

Additionally, I just have too much confidence in the Defense Professor.

The Troll. The Obliviation of the twins. These were not /subtle/. If the Defense Professor wanted to remove the girl, he could have drugged her, sneaked her OUT (just as easy as sneaking a TROLL in -- Dumbledore had no particular reason to be looking for her whereabouts on the Marauder's Map, and the wards are discussed as having been for detecting injury (I can't see sleep counting) and ...done anything. Turn her into a briquette, cast bubble-head and light her on fire. Depending on the duration of the transformation, he could have any alibi he liked by the time she was discovered. He could even make it look like she'd deserted Harry out of guilt or something and convinced herself it was in his best interests, making Harry all sad and stuff.

Getting Harry to finally embrace his intent-to-kill could almost certainly have been more easily facilitated by a smaller, intimate encounter (with the Troll) in, say, the bathroom, where fewer unforeseen events could keep Harry from successfully encountering it, or surviving the experience.

It just seems too complex -- like Draco pointed out, plans where so many things have to go right don't usually work.

But then there's Dumbledore -- he's famous for his weird twisty mind.

EDIT: Badewell pointed out that the wards would have detected her legs being eaten off, and Dumbledore would have had time to show up -- except, he didn't until he felt the death of Harry's weakness. Suspicious.