Ms De Piero joined people from around the world to pay respects to the Labour MP, who was only elected to Parliament last year.
The 41-year-old was shot and stabbed after holding a constituency surgery in Birstall, West Yorkshire.
Ms De Piero said: “Jo Cox - mum, proud Yorkshire lass, Labour MP for Batley and Spen - we miss you and we will never forget your ever-present smile. We grieve for your family and we heed the words of your husband Brendan and unite to fight against the hatred that killed you. RIP.”
World leaders, including Hilary Clinton - also paid tribute to Ms Cox, while scores of flowers were laid in her honour and the Union flag was flying at half-mast over the Houses of Parliament today.
A statement issued by her husband, Brendan Cox, said: In a statement, Brendan Cox said: “Today is the beginning of a new chapter in our lives. More difficult, more painful, less joyful, less full of love. I and Jo’s friends and family are going to work every moment of our lives to love and nurture our kids and to fight against the hate that killed Jo.
“Jo believed in a better world and she fought for it every day of her life with an energy, and a zest for life that would exhaust most people.
“She would have wanted two things above all else to happen now, one that our precious children are bathed in love and two, that we all unite to fight against the hatred that killed her. Hate doesn’t have a creed, race or religion, it is poisionous.
“Jo would have no regrets about her life, she lived every day of it to the full.”