Elowen Winter is beautiful and I think Ophelia and Juniper both go really well with it, especially Juniper. I'd go with Juniper Fawn though, I think Autumn as a middle name when your other daughter has Winter as a middle name might become a bit of a joke - everyone will ask you when your third girl mn Summer is coming along. Though I suppose they don't get mentioned together much so maybe not such a big issue.
Other first name ideas to go with Elowen:
Amberley, Amaya, Aphra, Astrid, Anoushka, Alannah, Ailsa, Avery, Anika
Bronte, Bryony, Brea
Cerys, Calliope, Calista, Celest, Calypso, Cassia, Cordelia, Christabel
Danica, Delphi, Dulcie
Everley, Eilidh, Evangeline, Evadne, Erica
Fenella, Fabia, Felicity, Francesca
Giselle, Genesis, Giovanna, Genevieve
Hermione, Harmony, Honor, Hebe
Isadora, India, Inez, Iris, Iona, Isolde, Iara
Jessamy, Jerica, Juliet, Jemima, Jonquil, Jacinta, Jocasta
Keziah, Katrina, Keltie
Larissa, Leonie, Lorelai, Laurel, Luana, Liara, Livia, Lois
Miranda, Mirabelle, Melinda, Meredith, Melody, Mika, Mala, Misty
Nova, Nyah, Nuala, Nia, Natasha, Noelle, Nadia
Octavia, Odette
Pandora, Paloma, Philippa, Piper, Pippa, Primrose, Persephone
Quinn
Rosanna, Ramona, Romilly, Robyn, Rivkah, Raven, Rhiannon, Rhiannyd, Raine
Saffron, Sorrel, Sorcha, Sylvia, Savannah, Saskia, Skye, Samaris, Sephora
Taryn, Tamara, Tamsin, Thalia, Tassita, Talitha
Verity, Vanessa, Vashti, Veda
Xanthe, Xanthippe
Yasmin, Ysanne, Yvette
Zipporah, Zeryn, Zillah, Zelda, Zia, Zara