Not showing for the arbitration greatly increase the odds of an unfavorable outcome, since there will be no one there who can tell or testify to her side of the story. (Lawyers, not having personal knowledge of the facts--I.e. not having been there--cannot testify as to what factually occurred). If the arbitration finds against her and orders her to pay money, then one of the options to force her to pay (if she does not pay voluntarily) would be to garnish her wages.