你好.很容易理解
She was sitting with her head buried in a newspaper.
===She was sitting （AND was ）readinga newspaper,with her head buried in it (it ==the newspaper).(语法：独立主格结构)
==She was sitting and was readinga newspaper,andher head was buried in it .（语法：两个简单句的并列结构）
翻译：她坐着,埋头读着报纸.