Complex sentence: As a young child, Charlotte was known by the same form of address as her mother had been in her youth, "Mademoiselle de Blois", but later on, assumed the style of "Mademoiselle de Valois".
Split into simpler sentences: As a young child, Charlotte was known by the same form of address as her mother had been in her youth, "Mademoiselle de Blois". Later on, however, she assumed the style of "Mademoiselle de Valois".