I do use my washing machine at night sometimes, as I do not have good organisational skills, and sometimes only realise the washing bag is full when it's too late to do it the next day as we need the stuff.
There are two walls between it and one neighbour, but she is never disturbed by anything anyway (health issues and is on drugs that make her sleep heavily), and her upstairs neighbours is far noisier than us anyway, at all hours.
And there is a wall and kitchen units between it and the other side's kitchen.
I can't hear it upstairs in our house with the kitchen door closed (other than in our room above it, and that's only because our mattress is directly on the wooden floor).
So I doubt her son (in the room adjoining our bedroom wall) could hear it at all; certainly wouldn't be loud enough to wake him up (we can hear when he wakes up, as he cries).
And she won't be disturbed while trying to sleep, as her room is the other side of the house.
So the only place in her house it might be possible to hear it would be her open-plan kitchen/living room, and if she's there then she isn't trying to sleep anyway (and is probably watching a programme which will be louder to her anyway).
I also never hear their washing machine, and that's against our joint wall, whereas ours isn't.
But I wouldn't hoover, that's much more intrusive; different pitch and moving around. That would wake my daughter up too (whereas the washing machine doesn't, even right below our bed).