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She called him to say she couldn't make it to the meeting.
Literal
She [topic-は] meeting [in-に] cannot-attend [quotative-と] him [to-に] phoned.
Indirect speech in Japanese routes the reported message through the quotative と: ~と電話する = 'call (someone) to say that ~.' The と here works just like the と with 言う or 思う — it attaches the embedded clause as the content. Notice 出られない: this is the negative potential of 出る ('to attend / go out to'), so 'cannot attend.' For meetings the verb 出る or 出席する covers attendance, with 出る being the everyday choice and 出席する the more formal one.