I think Onie could make a cute nickname. It sounds feminine to me. Also, it may be because of the similarity to yoni.
Ondine
IonaIoneOneidaOnoraOnaSidonieBellonaFionaWinonaLeonie
“She’s mad, but she’s magic. There’s no lie in her fire.” -
Charles Bukowski
http://www.behindthename.com/pnl/147561http://www.babynames.com/namelist/9852886