She is not an automation that merely does as she is told - at least not according to various statements by ex-PMs in their various memoirs and books.
And I think there is a difference in this instance as this is meeting one of the men who was involved in the murder of her husband's uncle ... I would not be willing to meet the murderer of one of my close relatives.
The provisional IRA statement on the Mountbatten murder, along with, it must be remembered, two entirely innocent teenagers, was utterly outrageous:
The IRA claim responsibility for the execution of Lord Louis Mountbatten. This operation is one of the discriminate ways we can bring to the attention of the English people the continuing occupation of our country.
See
http://en.wikipedia.org/wiki/Louis_Mountbatten,_1st_Earl_Mountbatten_of_Burma for this, and also for even more cynical and atrocious remarks attributed to Gerry Adams.
What the IRA did to him is what Mountbatten had been doing all his life to other people; and with his war record I don't think he could have objected to dying in what was clearly a war situation. He knew the danger involved in coming to this country. In my opinion, the IRA achieved its objective: people started paying attention to what was happening in Ireland.
Now, I am a supporter of a united Ireland, and have no regard whatever for Louis Mountbatten, but acts and statements of this order can never further any just cause. As stated in the 1916 Proclamation of the Irish Republic:
... we pray that no one who serves that cause will dishonour it by cowardice, inhumanity, or rapine. In this supreme hour the Irish nation must, by its valour and discipline and by the readiness of its children to sacrifice themselves for the common good, prove itself worthy of the august destiny to which it is called.
Blowing up an old man and two teenagers on holiday falls below these lofty aspirations.
However, outrages were committed on all sides, and if peace is to be made, the memory of these must not be allowed to prevent the process, just as was wisely decided in South Africa. I'm sure that many people who sign peace treaties do so at the same table as others who ordered attacks on non-combatants, or were responsible for the death of their relatives.
So the queen is either right, or has been correctly advised, to proceed with this meeting. Reasons for personal revulsion exist on both sides, and will only very slowly be conquered.