Lenore cradles her arm to her chest, even though the searing pain has dulled into a slight throb. Alaric is a steady presence at her side, but she can tell that this event has him stressed with how tense his posture is as he sits.
She also knows that he was shocked to see that pattern appear on her arm but not confused. He even pulled her sleeve down to hide it instead of trying to get a better look. With that, Lenore comes to the only conclusion that makes sense.
Alaric knows what it means for this pattern to appear on her. Whatever meaning it has seems to leave him at least a little shaken.