Catherine Marks from Married by Morning - Lisa Kleypas.
Catherine Marks, a spinster too young for her age, is a paid companion for the beautiful girls belonging to a wealthy family. She is a serious no-nonsense woman with a genuine interest in geography and other intellectual subjects that proper ladies shouldn't be concerned with. She has no family, apart from her employers and nobody knows about her past which still remains a mystery. She loves to write in her brown leather diary which smells like old paper and lovely memories.