As she will be too modest to say so, let me commend Barbara's approach (and Tom's) - if you get a chance to go to one of the Brown's sessions please do.
They provide a welcome which encourages the very inexperienced (my son was 8 and has never forgotten) and gives them a platform whilst encouraging respect for contributions which are genuinely intended. As a result their singarounds are usually populated also by extremely experienced singers and everybody has a good time.