[ Law & Legal ] Open Question : help on dismissal and appeal?

my daughter has been dismissed as her company say she did not phone in when she was off sick. She had told her manager and his deputy that she was going to be off (planned sickness following hospital appointment). They both deny knowing about this even though the rota was changed and my daughter was crossed off the rota. One of her colleagues said they heard her telling the manager she was going to be off. Another colleague crossed her off the rota and yet another colleague was brought in to cover her shift. Where does she stand for an appeal? Can she ask colleagues to provide written statements to take to appeal? She is not in a union. She has also reached the trigger point for sickness due to this ongoing problem.