So will Camilla be, if she is widowed. Neither she nor the former Queen Mother were hereditary queens; but they each were given the title because they were married to a hereditary sovereign King.
The difference is that Elizabeth Bowes-Lyon was the biological mother of the sovereign Queen Elizabeth II.
Camilla, no biological nor adoptive relation to William and not married to his father during his childhood, would not be entitled to use the style "Queen Mother." Rather she would be "Camilla, Queen Dowager" or "the Dowager Queen."
Excellent clarification!