。
She frowned at the woman.
Literal
She [topic-は] that woman [toward-に対して] face [object-を] frowned.
顔をしかめる (lit. 'wrinkle one's face') is a vivid set phrase for the facial expression of displeasure or pain. ~に対して ('toward, against, with respect to') marks the target — more formal and pointed than just ~に, suggesting 'directed at' that woman specifically. Together they describe an outwardly expressed reaction, the kind a witness or narrator might note when describing how an interaction went sour.