origin

[susieq2]

Who's she? The cat's mother? I know what it means but where did it come from?

[Quizmonster]

Nobody's certain, but click http://www.worldwidewords.org/qa/qa-cat1.htm for some enlightenment.

[Dusky]

As per the above link, I was chastised in this way many times as a child.  It was deemed more polite to use a lady's name or proper form of address (Mum/Grandma, etc.) rather than say "'she' told me" or "'she' said so".

 

The part about the cat comes, I think, from the fact that a cat which has had a litter is referred to just as a "she-cat", whereas other animals have other words like lioness, bitch, mare, sow, etc.  Not that some of these would be any more polite, of course...