I think 2 ee endings is fine, but Elodie and Rosalie combined tip into twee - but Leonie, Verity, Chloe, Phoebe, Lucy, Mary, Sophie or Hermione all work fine.
Marianne is lovely. Similar feeling names - Serena, Claudia, Francesca, Genevieve, Maryam, Harriet, Marguerite, Lucienne, Juliet, Adela, Rosanna, Rosalind, Rosamund, Philippa nn Pippa, Chrisabel, Annabel, Louisa, Josephine, Amelia, Cecilia, Alexandra nn Alix
Alternatives to Seren - Ffion, Jocelyn, Rowan, Robin, Linnet, Olwen, Catrin, Lois, Astrid, Ines, Iris, Arran, Carys, Annis
Slighter simpler classics to Elodie that also seem to work - Frances, Clara, Stella, Honor, Flora, Margot, Alice, Hope, Jane, Katharine, Charlotte,