She used to underline favorite passages to share with her husband. (Para. 1)
Meaning: In the past she often drew lines under passages she liked best so that she could remember them with her husband.
underline: vt. 1) draw a line under 划横线
The teacher told the students to underline the new words in the text. 老师要学生在课文中的生词下面划上横线。
2) give added attention to, so as to show importance强调；使突出
His leaving underlined his negative attitude toward the evening party. 他的离席说明他不喜欢这个晚会。
share with: give part of what you have to sb.
When the flood destroyed our house, our neighbors shared their house and food with us. 洪水摧毁了我家的房屋之后，邻居们让我们住到他们的房子里，并在他们家里吃饭。
Farmers often share their crops with each other. 农民们常常相互分享各自收获的东西。