She fell into a (dead) faint at the death of her son. 句中的at是什么搭配?（为什么要用at）

She fell into a (dead) faint at the death of her son. 句中的at是什么搭配?（为什么要用at）
She fell into a (dead) faint at the death of her son. 句中的at是什么搭配?（为什么要用at）

She fell into a (dead) faint at the death of her son. 句中的at是什么搭配?（为什么要用at）
at the death of 固定短语 “因为 由于”

固定搭配，有时候要记忆，而不是一直问为啥。