The traditional British way of doing this would involve Princes William and Harry. Her majesty would abdicate the throne and bypass Charles (unless he ended up face first in a vat of wine), naming William the new King. He would immediately travel to likely Canada, appointing Prince Harry as the “Lord Protector”, much like Cromwell.
Then Harry would act by edict, with the military to enforce his edicts. His first act would be to dissolve parliament, and imprison any who resisted. The military commanders would be authorized to conscript civilians as needed, and to bust up any protests or riots, as well as conduct summary trials and executions.
The first hitch in that fantasy is that the Queen has no constitutional power to alter the succession, which is determined by the sovereign parliament, not the monarch. The second hitch is that she has no power which could enforce such an overriding of the constitution even if she wanted to.