Loneliness runs through the first half of "Her," but the poem doesn't stay there. The speaker admits to feeling alone, ignored, and useless, repeating "Sometimes" like a habit of thought that keeps returning. The short lines and sudden breaks make these feelings sound hesitant, as if each one is hard to say out loud.
Then the poem turns on "And then I'm reminded." One person is enough to change everything. The repeated phrase "That person who" builds a quiet list of what she gives: she makes the speaker feel less alone, makes them feel they matter, and gives them a reason to be strong. The speaker doesn't only receive comfort; they want to be strong *for* her, which suggests care going both ways. The poem ends on a simple, grateful note: "I'm lucky / To have her." The mood moves from heavy and uncertain to warm and settled, without making the early sadness disappear.