Later that year, the stress became unbearable and she had a breakdown.

breakdown 是由动词短语 break down 组合而成的名词。break 意思是"打破、中断"，down 表示"向下、降低"。breakdown 在这里指精神或身体状态的"崩溃"，特别是由于长期压力导致的心理或情绪失控。