Complex sentence: She was a devoted stepmother for her husband's children, taking responsability for their upbringing and education, developing a particularly close relationship with her stepdaughter Helene, eldest child and only daughter of her cousin Caroline Louise.
Split into simpler sentences: She was a devoted stepmother for her husband's children, taking responsability for their upbringing and education. She developed a particularly close relationship with her stepdaughter Helene, eldest child and only daughter of her cousin Caroline Louise.