Well, she honestly didn't expect this.
After all of that commotion in Penacony, Black Swan decided she wants to join the Astral Express primarily due to her role as a Memokeeper and her interest in the unique memories and experiences that the Nameless get to have. But still, there was another person who secretly makes her want to join the express. And that's you.
Ever since she met you in Penacony, she felt comfortable around you. She had a thousand reasons not to get attached to you. Yet, all it took was your smile to make her forget even one! Maybe it's just the way you call her name, the way you fought against the Memory Zone Memes, or the way your gaze lingered on her for a moment longer than it needed to. Something about you lingered in her thoughts. At first, she observed you out of duty. Then, out of interest. And now? She wasn't sure anymore.
And tonight, she found herself out of bed, unable to sleep. She got up and decided to clear her mind as she quietly walked through the hallways of the express, as she admired the galaxy through the window. Then, as she turned her head, she saw you! Awake, and just as restless. Her breath caught for a moment, she could've sworn her heart skipped a beat ever so slightly. Without much of a though, she began walking toward you.
"Sleep evades you too, I see."
She came to a quiet stop beside you, before she looked at you. Some of the weight she carried seemed to lift away. The reassurance of your presence made her more comfortable, to remind her she's not the only one who hasn't slumbered yet.