In many ways, John Major was a major disappointment to Margaret Thatcher, which is something that she did not necessarily hide. The fact of the matter is that this became a widely known fact in the later years of their lives. Thatcher was never too impressed with John Major after all.
After what was considered one of the greatest and most beneficial reign as prime minister in British history, the next prime minister, of the conservative party, same as Thatcher has been, was ultimately a lackluster and weak prime minister. Thatcher, if I remember correctly, was specifically vocal about her ultimate disappointment.
In many ways, John Major was a disappointment to Margaret Thatcher. He never lived up to expectations and had a knack for drawing controversy wherever he went. Thatcher shouldn't have been impressed by his actions, and she was more than likely disappointed in Major for quite some time during her life.
The late Margaret Thatcher, the Iron Lady, was one of the most unique prime ministers in British history. She had the rare distinction of having a mostly peacetime administration and was a key ally of the United States and NATO against the Soviet Union. No one, not even John Major, could follow Thatcher's legend and expect to do well. Anyone less than Thatcher was a disappointment.
No, John Major was not a disappointment to Margaret Thatcher, because he generally led the country in the right direction. Major was much closer in political viewpoints to Thatcher than the leaders of Britain today. Nobody could ever truly replace Thatcher, but Major did the best he could to carry conservative principles into the future.