Paris no Isabelle (TV Series, 13 episodes, AniDB)

Requested before Jun 2019

The principal character is 15 year old Isabelle Laustin, other characters being her parents Leon and Marie, Isabelle`s friends Jean and his sister Marie, and Isabelle`s suitor, Captain Victor. When Paris is beseiged and Napoleon III`s army is defeated, Isabelle escapes to London, disguised as a boy, and engages in secret agent stuff. Source: anime-info.co.uk/tvdb/tvdb097.htm