A、Because she was ill-informed of the government’s policy. B、Because they were actually opposed to banning landmines. C、Because

It came as something of a surprise when Diana, Princess of Wales, made a trip to Angola in 1997, to support the Red Cross’s campaign for a total ban on all anti-personnel landmines. Within hours of arriving in Angola, television screens around the world were filled with images of her comforting victims injured in explosions caused by landmines.
  The Princess concluded with a simple message: "We must stop landmines." And she used every opportunity during her visit to repeat this message. But, back in London, her views were not shared by some members of the British government, which refused to support a ban on these weapons. Angry politicians launched an attack on the Princess in the press. They described her as "very ill-informed" and a "loose cannon".
  Opposition parties, the media and the public immediately voiced their support for the Princess. To make matters worse for the government, it soon emerged that the Princess’s trip had been approved by the Foreign Office, and that she was in fact very well-informed about both the situation in Angola and the British government’s policy regarding landmines. The result was a severe embarrassment for the government.
  To try and limit the damage, both the Foreign Secretary and the Defense Secretary gave corresponding statements respectively. For the Princess, the trip to this war-tom country was an excellent opportunity to use her popularity to show the world how much destruction and suffering landmines can cause. She said that the experience had also given her the chance to get closer to people and their problems.