Her letters to him might be the most revealing things she ever wrote. Her verse is famous for resisting the confessional urge, but in these letters she praises and damns other poets (she hated the Beats), speaks at length about her poems and fears, and repeatedly expresses her fierce love for Lowell, her friend and fellow poet: "Please let us not have falling-outs!"
At one time, his reputation overshadowed hers. But when feminism hit the English departments, that changed rapidly. Today, she and Lowell generally are considered at least equals.