After much consideration, she decided to back out of the project due to personal reasons.

back 在这里是动词，意思是"后退、撤回"。 out 是副词，表示"离开、脱离"的状态。 back out 是一个短语动词，意思是"退出、撤回承诺"，指原本答应参与某事但后来改变主意决定不参与。