Her article in theperage is here. She was born a Wriothesley in 1598, creating a mystery. Is this a 62 or more years-old Lady? Artists may flatter and aristocratic life could ease the ravages of age, but is this Penelope Wriothesley Spencer? Her article in thepeerage has another version of this portrait dated to 1669. Lady Penelope died in 1667, so the mystery could be solved if this is a posthumous portrait.
From Wikimedia. Also posted to the “Casual” Dress - 1641 to 1683 Album here.