We all have one: a gorgeous, sentimental piece of ­jewelry given to us by someone special that just isn’t our style. Even the late Princess Diana. When the 20-year-old earl’s daughter married Prince Charles in 1981, the Queen Mother bequeathed her a brooch featuring a duck-egg-size Sri Lankan sapphire set in a double row of diamonds. It was perfect—for someone else.“Diana wasn’t really a brooch person,” International Herald Tribune fashion writer and author of The Royal Jewels Suzy Menkes has said. “It didn’t really go with those clothes during the 1980s.” (Heavy pins and shoulder pads just don’t mix!) The new bride wore the brooch only twice before it seemed to disappear. Then a few years later, she boldly turned the jewel into the centerpiece of this breathtaking seven-strand pearl choker. Pearl chokers were a staple among the women in her family; her mother, grand