Just curious

I noticed that Charlotte Gainsbourg speaks with a British accent rather a French accent when she speaks English. That makes sense since her mother (Jane Birkin) is British. But does she have a British accent when she speaks French or is she totally bilingual? That's pretty unusual. (I speak Spanish with an American accent and a lot of my friends from South America speak English with a Latino accent, but it's very rare to not have an accent one way or the other).