Gunna your Mrs is ill-informed or being ripped off. If she's working a public holiday then it's double time; ordinary pay for working plus either time in lieu or payment of another day's pay. MA000089 - Vehicle Manufacturing,Repair,Services and Retail Award 2010
If this is not the case then either she's being paid under an agreement that compensates accordingly (I.e. a higher ordinary rate at all times) or her employer is breaking the law.
Public Holidays are one of the NESs and can't be excluded or ignored by any award or contract.
PS: Qld Ambos get time & half for ordinary hours on a public holiday...less than any other award I've seen. And that is an absolute fckin disgrace.