Terrible fastjet

My elderly mother missed check in by barely 5 mins and they wouldnt let her check in at the Harare airport. She was told she had to buy a new ticket for the next flight they wouldnt even consider the ticket she already had, I thought she would ahve had to pay a penalty or adjustment fee. When she made payment, the guy there pocketed the money. How does that work. I am disappointed in such service, they could have cut her some slack and let her check in......