。
She said that by way of apology.
Literal
She [topic-は] apology [as-として] so said.
謝罪として (as an apology) uses として to mark the capacity or function of her words — what she said served as her apology. そう言った (said so/said that) refers to something previously mentioned in context. 謝罪 (しゃざい) is the formal word for apology, more weighty than the casual ごめん or すみません.