Rachel and Leah by Orson Scott Card
Leah couldn't remember a time when her younger sister Rachel wasn't the darling of the family. Rachel was pretty, clever, and cute, whereas Leah's charms lay only in being obedient and hard-working. For years, Leah plugged along in her sister's shadow, until one day a handsome kinsman named Jacob showed up looking for a haven from his brother's rage. He found refuge in the home of the two sisters...and Leah fell instantly in love. As the three lived and worked together, Leah's emotions ran ever stronger. It was Rachel, however, that Jacob had eyes for. But Leah couldn't help but hope that Jacob would realize it was she, and not Rachel, that he should seek the hand of.