River thought of ignoring Simon, he was worrying for no reason, instaead she used her foot to kick a chair out or him to sit in and continued her story, which may have seemed like nonesense to them but to her she was telling of having fun on Serenity.
She didn't really want to stop to explain to simon that he was being silly. These people meant her no harm. Not even the big man with the guns or the lady who kept glaring... well she didnt' think so anyway...