( Bear in mind that Rose has Gates above her house, just like John. The boat wasn’t her only way out. )

Now you know that, and I know that, and Rose knows that….but her mom doesn’t know that.

So either a) her mom acted under the assumption that her daughter is dead and tried to escape herself

b) her mom didn’t give a shit on whether Rose was there or not, and tried to escape

And if she does know about SBURB, then that leads to

c) she ditched Rose figuring that she would be fine on her own to escape (or dead, who knows) and still just left

Meaning right now, there is a 1/3 chance that her mom isn’t a complete dickbag