「」。
With an apologetic look, she said 'I couldn't eat it.'
Literal
She [topic-は] apologetic-seeming [manner-に] 'couldn't eat' [quotative-と] said.
Small but delightful mix of grammar. 申し訳なさそうに breaks down as follows: 申し訳ない ('inexcusable, apologetic') is an い-adjective → 申し訳なさ (the さ-nominalization, 'the quality of being apologetic') → 申し訳なさそう ('looking apologetic,' using the appearance suffix ~そう) → 申し訳なさそうに (the adverbial form). The ~そう ('looks/seems') attached to a negative い-adjective requires the さ: not 申し訳なさそう from 申し訳ない but specifically 申し訳な + さ + そう (ない → なさ → なさそう). This is one of the trickier spots in intermediate grammar. The ~そうに adverbially modifies 言った ('said').