Young Adult historical novel about the childhood/teenage years of Margaret Plantagenet of York, who later became Margaret Pole, and her brother Ned (Edward, Duke of Warwick), at the end of the War of the Roses and beginning of the Tudor period.  It starts in the court of her uncle, Edward IV, after her father (George, Duke of Clarence) has been executed for treason, and ends with her brother’s execution and her romance with Reginald Pole.  My memory is that the heroine is known as Meggy or Peggy. I probably read this in the early 60s, but it might have been written in the 30s, 40s or 50s. I thought the author might be Elizabeth Janet Gray, Rosemary Sutcliffe, Margaret C. Leighton, or Elizabeth George Speare but can’t find anything that seems to match this story among their titles.