2 Books Found

Based on your description:

"This is all I can remember: A girl grows up in an inn with her family, but she is ostracized due to her ugly appearance and broad shoulders/tall height. Her sister and parents have normal appearances and judge her/belittle her too. She gets the opportunity to live and work at the castle in her land and meets the prince there. He sees her beauty and they become friends. She has thick black hair and a beautiful singing voice. There is a woman who is unkind but beautiful that manipulates the heroine into using magic to alter her appearance. The heroine either before or after that meets an elf who calls her beautiful and shows her that she actually has hair in a blue-black color that only elves can see. The prince traveled with her on a journey to meet more elves that live in a mountain and learn about herself. On the journey they get attacked by orcs."