AUSTRALIA: Should step-mom be called "mum"?

Interesting case coming out of Australia according to News.com.au. A couple who have been litigating their divorce for six years had one issue left to settle: the issue of whether the new wife should refer to herself as “mum” in reference to the stepdaughter. The child’s biological mother and ex-wife (the plaintiff in the action)  felt that she is the only “mother” of the child and that any references to “mom” or any derivatives of that name should refer only to her, the real biological mother, and not the new wife.
The court in Adelaide basically declined to grant the biological mother’s/plaintiff’s request that the step mother cease and desist in referring to herself as “mum” in relation to the step-child. The step mother even called herself  “mummy-d” and signed off on the child’s school reports as “mum.”
I agree with the biological mother. And in fact, I have seen many divorce cases where it is a part of the stipulation that the child is NOT to call any other individual “dad” or “mom” except for his  or her biological parent. This is very critical and I am surprised that the court was not sensitive to this woman’s request. It is in the best interest of the child, furthermore, to be clear on his or her parentage and to not be confused with all these mommies. You have ONE mother. You have ONE father. Period. And frankly, some of these step parents are bullies and instigators and they encourage the child to call them by this moniker to get at the ex. This is not cool. Not to say all step parents do this. But some do and it is not cool. There has to be boundaries. There has to be respect for the biological parent. It is good for the child that lines are drawn and are not crossed; and it is good for the relationship between the former spouses. Besides, at the rate at which second marriages implode, what happens if there is a third marriage? Or fourth? Now the child has how many people to call “mum” or “dad”?
This is ridiculous. I can’t believe the court failed to see beneath that new wife’s treachery. She’s trying to steal that ex-wife’s child’s affection and alienate the child from her biological mother and usurp that biological mother’s authority and place in her daughter’s affections. The blind can see this, why couldn’t the judge?
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