Zara Tindall, the accomplished equestrian and daughter of Princess Anne, has been competing at the Blenheim Palace Horse Trials in Oxfordshire. The event, which began on September 19 and concludes on Sunday, has seen the 43-year-old Olympic silver medallist in her element. Zara was spotted riding her horse Classicals Euro Star on Friday, donning a navy jacket, white jodhpurs, and a riding helmet. The mother-of-three, who secured a silver medal as part of the British Equestrian team during the London 2012 Olympics, has been at the event for several days. On September 18, she led her gelding, Cl…