I don't think Sadie is a common name? I only know 2 - one teen and one adult.
I love Sadie, Ava and Sophia. Lily is nice enough too.
Other ideas:
Astrid, Alyona, Anika, Avery, Adele, Athena, Asthina, Asha, Acacia, Averil, Bronte, Bryony, Billie, Celest, Cecily, Christabel, Coralie, Carmen, Cadence, Dulcie, Danika, Devora, Daphne, Della, Delphi, Etta, Effie, Enya, Erica, Esther, Elina, Elianne, Fenella, Fabia, Faith, Giselle, Greta, Hazel, Halle, Hebe, Honor, Ivy, Ines, Joanna, Kiki, Keziah, Kendra, Lorelai, Lyra, Leona, Livia, Mala, Mika, Marta, Melody, Nyah, Naomi, Ottilie, Posy, Polly, Rosina, Robina, Rowena, Ramona, Saffron, Sorrel, Skye, Sabrina, Saskia, Serena, Taryn, Thalia, Tamara, Tessa, Verity, Vashti, Xanthe, Yvette, Zeryn