Complex sentence: Smoczynska had also wanted to build on a retelling of "The Little Mermaid" by Hans Christian Andersen, and developed her idea of mermaids from tales of the 14th-16th century that described them as the sisters of dragons, and hence made them part monstrous.
Split into simpler sentences: Smoczynska had also wanted to build on a retelling of "The Little Mermaid" by Hans Christian Andersen. Smoczynska developed her idea of mermaids from tales of the 14th-16th century that described them as the sisters of dragons, and hence made them part monstrous.