What about the legal system in the UK/Canada/Australia that have it in constitution that she as a veto to the passing of new laws as a balance.
Could the system be made not to require the monarchy anymore? Sure, it’s purely ceremonial and has been for her entire reign, but to say that the monarch can make that decision at whim on behalf of 15 countries is just not true.
You're right that it would require international cooperation, though: the British parliament doesn't legislate for the other Commonwealth Realms any more.
Nonsense. Cromwell had to fight and win a very bloody civil war to abolish the monarchy. Despite that it was still restored after his death.
The Right of Parliament controls the constitution of the UK and has done since the Glorious Revolution of 1688, not the current reigning monarch.