。
She's out of breath from playing basketball.
Literal
She [topic-は] basketball [object-を] do-and breath [object-を] is-cutting.
息を切らす ('to be out of breath') is a fixed verb-object collocation literally meaning 'to cut one's breath' — Japanese conceptualises breathlessness as the breath being severed rather than the lungs being short. The auxiliary ~ている here marks a resulting state: she's not actively cutting her breath now, she has done so and remains in that breathless condition. The te-form バスケットボールをして supplies the cause, working a bit like English '-ing' or 'from': playing basketball is what brought her to this state.