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 劃橫線
The teacher told the students to underline the new words in the text. 老師要學生在課文中的生詞下面劃上橫線。
2) give added attention to, so as to show importance強調；使突出
His leaving underlined his negative attitude toward the evening party. 他的離席說明他不喜歡這個晚會。
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. 洪水摧毀了我家的房屋之后，鄰居們讓我們住到他們的房子里，并在他們家里吃飯。
Farmers often share their crops with each other. 農民們常常相互分享各自收獲的東西。