Celtic choices:
Alys, Aoife, Bethan, Bonnie, Branwen, Bridget, Delyth, Eleri, Elowen, Elspeth, Fenella, Fiona, Gwen, Gwyneth, Iona, Kerensa, Lowri, Maelys, Manon, Maura, Meleri, Rhian, Tegwen
Names like Estelle, Ottilie, Etta, Marianne, Matilda, Esme, Anouk & Edie:
Ada, Augusta, Beatrice, Cecily, Clémence, Clio, Colette, Delphine, Dinah, Elodie, Elsa, Hebe, Henrietta, Ivy, Jemima, Leonie or Léonie, Lillian, Louisa, Nancy, Rosa, Sadie, Tabitha, Verity, Willa
A few others just in case they take your fancy:
Annora, Felicity, Hester, Honora, Pippa, Saskia, Verena