Complex sentence: Although Rebecca strives to win Miranda's approval, she finds it hard to live up to the older aunt's high standards, as she has to fight against Miranda's view of her as "all Randall and no Sawyer".
Split into simpler sentences: Although Rebecca strives to win Miranda's approval but finds it hard to live up to Miranda's rigid standards. Rebecca is up against Miranda's view of her as "all Randall and no Sawyer".