。
I wonder what ever happened to her.
Literal
She [topic-は] how became [I wonder-かしら].
かしら is the feminine counterpart to かな — a sentence-final particle expressing soft, self-directed wondering ('I wonder if...'). Historically and stereotypically associated with women's speech, it now reads as a marker of feminine, slightly old-fashioned register; younger speakers tend to default to かな regardless of gender. Pairing かしら with どうなった gives the question its gentlest, most introspective shading — a quiet 'whatever became of her, I wonder' rather than a pointed inquiry.