Elizabeth of York was the wife of King Henry VII and mother of infamous Henry VIII. She died in 1503 making this likely a posthumous portrait.
She is holding a white rose, a politically charged gesture after the "War of the Roses" between the Tudors (who won) and the Plantagenets. She was Elizabeth of York, a Plantagenet, who married one of the victorious Lancastrian Tudor generals who became King Henry VII. Time to bury the hatchet, and not in one another's heads. Religion would provide plenty of scope for conflict during her son's reign and the reigns of her grandchildren.
Her Wikipedia article is here.