。
I wonder who she is.
Literal
She [topic-は] who [I-wonder-かしら]?
かしら is a sentence-final particle expressing soft wondering — 'I wonder if / who / what.' It's traditionally feminine speech, though men do sometimes use it; in modern Japanese かな is gender-neutral and far more common, while かしら carries a slightly old-fashioned, refined, or feminine flair. Functionally interchangeable with かな (誰かな = 'who is it, I wonder').