My bad, as pointed out above I'm completely wrong with what I said. I've take my own advise and now read the Oneworld website, and it clearly states the following -

"If your Oneworld frequent flyer tier status is Emerald or Sapphire, or you are traveling in a First or Business Class cabin on any oneworld member airline, you can access some 650 airport lounges throughout the world.
This means you can relax or catch up with work in comfort and style before departure, regardless of which oneworld member airline you choose to fly with."

Luckily I don't control the access to airport lounges, or I would be as wrong as the staff at the Cathay & Qantas lounges. Suffice it to say, why don't the airline staff know their own access rules?

Again I apologise for giving the wrong info, I do seem to remember is was this way once, but clearly things have changed and for the better too.

Good luck to you Mum for the rest of her trip. Hope she gets to enjoy more Oneworld lounges on her travels.

Cheers & Sorry