I go back and forth on this one. Sometimes I can only see it as a masculine name (which is odd because I love NNs like
Charlie,
Teddy,
Micky, etc. for girls), but then other days it sounds so sweetly old fashioned and I can't help but think of
Billie Holiday. Either way, if I heard someone talking about a
Billie I would never think to question whether it was a little girl or boy. On the plus side, if she does decide that
Billie is to masculine
Willow,
Willa and
Wilhelmina (or even
Mina) are fantastic names to fall back on.