As soon as they arrived at Kwall and she was helped out of the carriage Naiari noticed that Kael had disappeared. Most likely as soon as they got on the grounds because she did not even get to see him leave. She was led up to her room not his and that made her raise her brows, thinking that he did not want her in his room.
She figured out that his actions probably meant that he did not want to be around her, she had sensed that he seemed to have withdrawn from her and that made her think that he probably preferred Yvette's looks to hers and was pained that she was the one that he was stuck.
It should not hurt her after all virtually like everyone else in her life had felt that way but the pain from his seeming rejection was acute.