I really love
Rose. It's so timelessly elegant, and it can fit any person and any age. So many of the variants are gorgeous, too.
I'd definitely consider using
Rose. I'd use a combo like
Rose Eugenie or
Rose Imogen.
As a middle name it's definitely a filler, so I'd want to spice it up a bit:
Perdita Rose or
Imelda Rose.
Penelope Rose is also stunning to me, even if
Penelope is a bit more common than my other ideas.