I disagree. Whether or not any or all of the Royal Family are believers is not the point. The point is that this is just a PR stunt. The Queen must act within the constitution and that meand she cannot be petitioned except through her ministers. Oh well.
But the Queen does talk directly to the Archbishop of Canterbury, right? I suppose then it would mean that the ABC would have to bring the question up with Queen Elizabeth, the current "Defender of the Faith".