Two stones thrown at Buckingham Palace windows during a suffragette protest more than a century ago and saved for posterity represented “hope to the women who threw them”, Queen Camilla has told equality campaigners.

While some of the suffragette’s more destructive tactics could not be condoned today, Camilla said there was “sermon in the stones” that had cracked two window panes but were kept by the royal family.

In a speech as president of the Wow (Women of the World) festival she told guests including Dame Helen Mirren, Doreen Lawrence, Spice Girl Mel B and Dame Kelly Holmes: “I would like to begin with a ‘show and tell’.

“I have here two stones that, on 27 May 1914, were thrown at the palace during a suffragette protest. The label on this one reads: ‘If a constitutional deputation is refused, we must present a stone message.’ This one says: ‘Constitutional methods being ignored drive us to window smashing.’

“The Times reported two days afterwards: ‘Between 11 and 12 o’clock on Wednesday, two women succeeded in evading the sentries at Buckingham Palace and entered the quadrangle. They threw stones at the windows and broke two panes of glass before the sentries intervened.’”

The women were arrested, but the palace’s master of the household refused to prosecute, and Queen Mary, wife of King George V, kept the stones, Camilla said.

“I thought today we might, to quote Shakespeare, find “sermons in stones”, she added. While not encouraging her audience to take similar actions, she said, and “while the more destructive steps taken by the suffragettes could not be condoned today, I wanted to show you these stones because of what they represent.

“In 1914, I believe, they represented hope to the women who threw them – hope that, in the future, they would not be victims of their history, nor of the social and economic forces that were ranged against gender equality. Above all, they represented the hope that it was possible, as Christabel Pankhurst said, “to make this world a better place for women”.

She told the Buckingham Palace audience, which included some schoolgirls, that 110 years later they had been invited because they too represented hope for women in the present and in the future.

Camilla was presented with her own personalised Barbie doll and joked that it made her look 50 years younger. Holding the miniature version of herself during the event celebrating Wow and International Women’s Day, she said: “You’ve taken about 50 years off my life – we should all have a Barbie.”

The one-off Barbie was dressed in a scaled down version of an outfit worn a number of times by Camilla: a blue Fiona Clare dress, black cape by Amanda Wakeley and Eliot Zed black boots. The doll’s hair was closely modelled on Camilla’s curls as was the jewellery worn by the toy, which featured a Wow badge also worn by her.

The presentation was made on board the Wow Girls festival bus, which has toured the country promoting gender equality and made a final stop at the palace where Camilla toured it with Queen Mathilde of Belgium and the Duchess of Gloucester.