Is Ellyn pronounce like Ellen? If so, be prepared to spell it every time you say it.
Willow is not 'rare' but it does sound nice.
Maybe you might like Alice, Amabel, Amy, Ann(e), Annis, Audrey, Beatrice/Beatrix, Catherine, Cecily, Christabel, Clarice, Clemence, Colette, Damaris, Diana, Dinah, Dorothy, Eden, Edith, Eleanor, Elizabeth, Ellis, Emery, Esther, Everill, Faith, Felice, Felicity, Flora, Florence, Frances, Freda, Hannah, Helen, Hester, Honour, Hope, Ismay, Jacqueline, Jane, Jays, Jesmond, Joyce, Kinborough, Laura, Lettice, Lillian, Lilias, Lucy, Mabel, Madeline, Margaret, Marian, Mariel, Martha, Matilda, Maud, Mercy, Millicent, Miriam, Nest, Olive, Phoebe, Phyllis, Rachel, Rebecca, Richemay, Ruth, Sabine, Sessley, Sibyl, Tace, Ursula, Violet, Wilmot, Winifred, Zenobia? (All used 1450-1650 - homepages.rootsweb.ancestry.com/~oel/givennames.html)