It's either a 2016 or 2017 movie.
So two secret agents (a woman and a man) were in the War and wanted to kill someone. I think a German.
They were in France.
They fell in love and got married. She gave birth during the war.
At work they told the man that the woman is stealing information from them and send them at Germans.
She confesses and kills herself so they don't kill both of them and the little girl (is still a baby).
At the end it shows us, her writing a letter for her daughter.