It was habit, pure and simple, a case of a potential issue not being dealt with, nipped in the bud early enough.
ALL DC will want to snuggle in, and that occasional snuggle will become a habit, the longer that goes on, the harder it will be to be righted.
We've been rather unsettled this past year, leaving an expat life abroad, coming home here, living at my mums for a while, then moving to rented. DH was sorting stuff out in the expat location, so I was alone with DS (4) for about 8m.
DS used to sneak into my bed, but initially because of my mum and her DH I couldn't really risk him kicking off when I took him back to his own bed, so I let him stay in my bed.
When we moved, he was unsettled I allowed it to continue, but told him that he has his bed and I have mine. Then I told him that he had to sleep in his own bed when he had school the next day. Eventually he broke himself of the habit.
He still comes in if he's had a bad dream, but that is rare.
Sadly, the little girl knows she's got away with it in the past and the mum has not tried to correct it. She's pushing all her mum's buttons, cos mum in the past has caved.
As dreadful as it looks, the tantrum is designed to get on the mother's last nerve, it is just her trying to get her own way. If there were any other issues, they would have been identified and dealt with by Jo Frost.
It is of course heartbreaking to see a little girl cry like that, to sleep on the floor, but it was her doing. The mum needs to be consistent. All of this is for the girls own good.