The question you ask, is generally that of how MB could have been last seen, and then not seen again.
I do have an answer with a logical explanation. My idea isn't one that necessarily wows, but it can work. And the problem is, what are the alternatives? I'm not challenging you, or others, but only working this in a mathematical mindset where you take what you have, work within the limits, and see where that goes.
On the map below ...
The blue arrow, showing MB's entry and early steps in the building, is fact.* LE has told us she (a) entered the SW doors, (b) went up the main hallway being seen by cam, (c) at some point was no longer seen, presumably too far from cam.
* We don't know if she stops where this arrow does, or goes much farther. But she should have gotten approximately this far, if not farther, per LE's words.
So if she is out of sight there or somewhere farther up, and ends up found in "the southwest corner of the interior of the building" without being seen (as LE has sworn under oath), then how and where? It has to be a place where she can get there unseen and also perp can leave unseen and leave by the kitchen door.
I have made some guesses that could fit. Is there a better one? Not that I see. But I'm listening, just in case.
One possibility is that she's attacked/grabbed as she passes the corner of P1, and shoved into the auditorium. Another is that it happens at P2 and she's shoved into the kids room. A third is farther up the hall at P3. In each of those places, there is a hiding corner and a door out of the hallway as well. In each option (*graphic detail warning*) it's possible that the initial attack slowed her badly but she tried to escape, and was trying to flee while being pursued in a damaged state and then finally being beaten to death where she was caught. That allows for movement, without carrying. But, maybe she was carried or dragged a ways, that could fit just as easily.
But in any event, each of those scenarios is fully off camera view, and allows a path from where she was last seen, to some SW place.
As for those theorized ideas for where her body was found, each can fit generally into the given description of "the southwest corner of the interior of the building." And I don't see any better ones, to get to and leave from, unseen by cam. Just like the "porte-cochere vs awning" discussion, we have to be liberal in our allowance for what LE meant by that description, because what was meant is what
they were thinking of, even if the words could be used to indicate other specific places.
The kids room location, that's really near to the SW of the entire building, but not quite in the precise absolute exact corner itself. But it's in that area. And there's a possible off-cam route to the kitchen door exit.
The auditorium location works if, to them, the expression
"interior of the building" meant the auditorium (and that's possible, since that's the most interior area). And from there, there's a possible off-cam route to the kitchen door exit.
I'm certainly open to any other areas that fit LE's description, in any broad way, but only if they also could have been accessed in an unseen fashion from where we can last place her in the hall, and only if there's a way to get from there to a kitchen door exit off cam. So far, these are the only ones I can come up with.