What difference does it make if the strangulation was premeditated? None is the answer.
It's likely people have carried dead bodies before or how else would you move one?
Even if you used a car you'd still need to carry the body to the car.
I don't know what the twins were doing when Maddie could have been murdered.
Corrie McKeague was a grown man when he went in the bin & no one ever found him.
Nothing you have said disproves this possibility & no investigative force has proven abduction.
I asked whether or not you thought the murder was pre-meditated or not because if so I could envisage it taking place with the minimum fuss, however if it was as a result of Kate flipping out and flying into a murderous rage I would imagine there would be at least some accompanying noise, eg the screaming of the child that triggered the rage, or some shouting beforehand, or some upset from the twins witnessing a horrible incident. But no, bat-eared Pamela Fenn must either have had her hearing aid switched off during the murder or the rage was all silent and unwitnessed by the twins, and Gerry's reaction on discovering his little girl had been murdered by his wife was also very subdued. No sobbing, no crying, no arguing, no panicking. How very civilised!
Nothing I have said disproves anything, but IMO it does shine a light on how improbable the scenario is. Kate, enraged, silently murders her child. Her husband is cool enough with this occurrence to hatch a plan with her which involves staging an abduction. The plan includes leaving the apartment unlocked, allowing friends to perform checks on the kids, raising the alarm during dinner, sending the friends one way while Gerry retrieves the corpse from its hiding place somewhere unspecified then, while everyone is in a blind panic looking for a missing child, carries the corpse through town (after having changed his trousers of course), is seen by half a dozen people, then conveniently finds a bin in which to dispose of the corpse, a bin which is also conveniently emptied within a few hours, then returns to the apartment with no one having noticed his absence, changes back into his jeans, then submits to the gaze of the world's media within 24 hours of the disposal (knowing that at least half a dozen people saw him carrying a child at the time the alarm was raised), and subsequently spearheads a massive fraud to make a million, whilst all the while striving to keep the public's attention focused on the crime that he himself committed together with his wife. Yes, all very logical and plausible I'm sure. Dismiss this all as affle as I'm sure you will, if you went to the cinema to watch a film in which this was the plot you'd sneer at the ridiculousness of it all. Well I would anyway!