Unfair cancellation of return flight at CT Airport

My daughter missed her BA Cape Town to Durban flight early this morning and was forced to pay FULL PRICE for another ticket AND then was told that because she had booked both tickets with BA, she had ALSO LOST THE RETURN TICKET FOR MONDAY ! She was told by people at the Cape Town airport desk that she no longer has her return flight and so she called me from the airport in tears. Both tickets will now cost even more than the original flight I paid for, adding around another 3k to the original flight cost. We still have to book her Monday return flight, but if this is the case and nobody offers a compromise, I will make sure that we never, ever fly with BA after this unfair policy which had her sitting crying in the airport a few hours ago. How can it be fair to cancel the return flight? They have her cell number so why did nobody call her first? She was told that other airlines do not treat people like this.