Well, hopefully someday soon the Queen will allow a royal biographer full access to the Royal Archives to write a definitive biography of her mother so we can learn more.
We do know the Queen Mother was very disapproving of Wallis Simpson from the very moment they first met. Most royal biographers agree, however, that she never was interested in marrying David, nor was he interested in her. She was reluctant to marry the Duke of York as she knew the heavy burden of becoming royal and the duty it would entail. Given the era and standards of the society she was raised, it is inevitable that Elizabeth would take exception to a pushy American like Wallis Simpson in the royal circle, compared with a quieter Lady Furness as a mistress.
Similarly, it seems the Queen Mother did not mind her grandson, Prince Charles, was very comfortable with his mistress, Camilla Parker-Bowles, often allowing them to use Birkhall when she was not in residence. However, she was equally adamant that the Prince and Princess of Wales not separate and remain married for the sake of the throne. She blamed Diana for failing to keep Prince Charles happy and by her side and was convinced she was "unsuitable" to be Queen Consort.
After the separation, it seems the Queen Mother began to change her tune a bit and started becoming very dismayed with her grandson's tendency to act like his Uncle David and disregard his duty to the throne. She still disliked Diana's tendency to manipulate the media and felt she was damaging the monarchy, however, she also understood Diana's importance to the monarchy and her role as the mother of a future king. After the Panorama interview, it seems the Queen Mother irrevocably changed her view of Diana as a liability who must be jettisoned completely from the royal family.
With regard to Camilla, the view of the Queen Mother was clear. She was unsuitable to be a member of the royal family and must never be allowed to marry Prince Charles. She refused to receive her privately nor would she allow Charles to discuss the matter. If she were alive today, Charles would still be single.