I'm with Carole on this one.........100%

"Personally i think it is rude when a person does not even acknowledge you spoke, simply to say nothing is rudeness. Even a simple nod just to let the other person know you are listening or heard them is better than nothing."

Guess it could just be one of those downunder things.

If I had a wife that treated my mother like that, I'd probably bop her.
Maybe you should talk to your son, and see what he says. Maybe then he can have a word with her on the side.

As for MIL's, some people say mum, others call them by their first names, others have pet names for them. It's really what both are comfortable with I guess.