Most of River's time on board the Banshee was spent in the cockpit, or in her bunk. When everything was quiet and the rest of the ship was asleep - or at least otherwise occupied, in the case of their vampire captain - she would slip out into the corridor, bare feet leaving residual footprints in momentary condensation along the cold metal floors. Sometimes she would sit just outside whatever room the rest were in, listening from a distance to their conversations and dreams. Sometimes she would climb into a secret nook in the engine room and listen to the thrum of the ship's machinery, tracing histories of journeys past and making friends with the squad of droids.
She had mostly stabilized, recovering from the initial trauma of being ripped from one universe and handily thrown into another. Being away from Naboo and its large population centers had been good for her, quieting much of the noise she had forgotten how to block, once again giving her a point in reality to ground herself to. Selene's linear mind certainly helped with that as well, whereas Quill's was good for a laugh. But it was Sara's mind that was still puzzling to her; somehow it seemed to be jumbled and not at the same time. Quantum states manifested in psychological form, River had figured, but had mostly kept her distance, afraid that it might draw her back into instability.
Of course, she'd felt when Sara disappeared, something she'd read about happening on the Holonet. She'd felt her reappearance, too, and it had almost knocked her to the floor from her current hiding place in the shadows. Whatever had happened, it hadn't been good. River could feel Sara's pain from the other side of the ship. It hurt her in a way she'd never experienced before; not when Book died, not when Wash died. They were sudden, but not instantaneous, and it made River fearful that one day she might be sent back home, too - only to learn that she'd lost Mal or Zoe or Kaylee or Emma... or Simon.
As she climbed down out of her cozy nook, feeling the need for a change of scenery, she focused her mind on not thinking about the hypotheticals. The 'Verse had already tried to take Simon from her once, and she had stopped that. She could do it again. Here she was okay, because she knew that there, Simon was okay. But if that ever changed...
She was so lost in thought, she didn't even realize she'd turned the corner, until she was seized by a sense of imminent collision. Freezing in place, she looked up to see Sara, looking exhausted. All the thoughts that had been swirling in River's mind fell quiet as she tried to find the right words, the kind that everyone else always knew, the ones that tried to make it better.
"I'm sorry about your sister," she finally said softly, looking down at her toes. "And your friend."