Hello and thank you for your question.
It sounds like a type of workplace bullying. Taking legal action for bullying without any other context is possible but it your wife's case would become stronger if you can demonstrate that the bullying behaviour is arising because of descrimination on a prohibited basis under state or federal anti discirmination laws. Although it is not clear which state you are in, all states of Australia have laws which prohibit discrimination on the basis of gender, race, religion, and most also have laws agains descrimination because of family obligations.
You can read about bullying here, and may receive some further advice from the Fair Work Ombudsman if you contact them:
At a minimum, I would suggest your wife start keeping records of any occasions where she feels she is receiving unreasonable treatment or demands, as this may prove useful should legal action later be necessary. Given the long history of problems, and the suspicion they are at some point potentially soon going to force her out of her role, I think it very much may be worthwhile engaging an employment lawyer to review her case in more detail than can be done through a service such as this.
I trust the above assists
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