Originally identified as Lady Jane Grey, perhaps Margaret Douglas
Somerley Estate

This painting can be found in the following:

A Queen of a New Invention: Portraits of Lady Jane Grey Dudley, England’s ‘Nine Days Queen’ by Stephan Edwards.

Tudor: The Family Story by Leanda de Lisle.

The Lost Tudor Princess: A Life of Margaret Douglas, Countess of Lennox by Alison Weir.