Postcards idea

You find two old postcards in your great grandmother's belongings. One is a photograph of her. Another is a postcard of a fashionable lady of the time, maybe a singer or an actress, and she looks like your great grandmother.
Are they the same person?
Could your great grandmother have had a double life? Two names? Two identities? Why? Did they have a secret?

Write a story about someone who has two identities.