The Lady of the Rivers (The Plantagenet and Tudor Novels #1) by Philippa Gregory

Jacquetta, daughter of the Count of Luxembourg and kinswoman to half the royalty of Europe, was married to the great Englishman John, Duke of Bedford, uncle to Henry VI. Widowed at the age of nineteen she took the extraordinary risk of marrying a gentleman of her house-hold for love, and then carved out a life for herself as Queen Margaret of Anjou's close friend and a Lancaster supporter - until the day that her daughter Elizabeth Woodville fell in love and married the rival king Edward IV.