My niece is named E l o w y n. O a k. so obviously this one is my favorite 
I also love Elowyn Rae, Elowyn Adelaide, Elowyn Verity, Elowyn Marigold, & Elowyn Sparrow! As a side note, I know an E l o w e n. O p h e l i a. & I think she’s gorgeous as well!
Other middles:
Elowyn Avonlea (Oak)
Elowyn Josephine
Elowyn Odelia
Elowyn Harvest
Elowyn Zipporah
Elowyn Alcott
Elowyn Meadow
Elowyn Olinda
Elowyn Prairie
Elowyn Miriam (Oak)
Elowyn Agatha (Oak)
Elowyn Oriel
Elowyn Junia