Are there any au pairs who would be happy to just speak their own language (French) to the children rather than English?

We are looking for someone who is interested in just speaking French to our daughter as she is bilingual and already hears English from us and around her. I understand most au pairs want to travel to improve their language skills and so they could speak English with us and do English lessons but we are really hoping to find someone to speak French to our daughter. Has anyone got any experience of au pairs helping their children with learning a language? Thanks, Jennifer