。
She looked like she was about to faint.
Literal
She [topic-は] at-any-moment faint-do [appearance-そう] was.
今にも ('at any moment, on the verge of') pairs naturally with the visual evidential ~そう to form a stock template for imminent events: 今にも~しそう ('on the verge of doing X'). The past-tense そうだった freezes that imminent moment in the past — 'looked at any moment about to.' 卒倒する ('to faint, to collapse') is a fairly literary alternative to 気を失う ('lose consciousness'); 卒倒 itself is a Sino-Japanese compound that adds dramatic weight to the description.