I agree with Q & CET, if you don't understand the symbolic function of performing a ceremonial office, better to leave it to those who DO, to decide whether or not it is appropriate for any particular party to fulfill that public duty, or not.

I'm not a Royalist myself, but I respect the feelings of those for whom certain long-standing traditions have a deep meaning, purpose and importance. Especially those (and the families of those) whose lives have been lost in service to a greater collective cause.

I also sense a degree of 'She's just a Woman, so she shouldn't do that!' in Gnu's post. To which I'd be inclined to refer him to any amount of English Queens, who would take exception to that assumption with a summary "Off with his head" ;-)