its depend brother your mother visa will complete its six month in december,but we dont know exactly when umra visa will open and some time agents not give on time it happen to me last year,so its better in start of december you try to get one month extension for your mother visa,if there will be any delay in opening of umra visa you will not have any tension about expirey of qatar visa.first get qatar visa one month extension in december then take re-entry for saudia and then give to agent for umra visa,INSHALAH you will get visa