If I understand correctly, Marina has chosen to sing in English to provide her with the broadest possible audience, as well as opportunities. Off the top of my head, the only French song I remember her singing is La vie en rose when she was 13 years old.
If you search YouTube for Marina Kaye, you'll find a lot of performances she has done. She always sings live and never lip-syncs. She truly has a wonderful voice. Her album is now certified platinum in France.
Here she is doing 3 songs from her album "Fearless".