Because when her husband was alive she was The Queen Consort, and on his death she should have been Queen Elizabeth.
But she chose the title Queen Elizabeth, The Queen Mother to avoid confusion with the new Queen Elizabeth.
She wasn't just the Queen's Mother, she was a queen.
The term queen mother denotes a queen dowager who is the mother of the reigning sovereign, irrespective of sex. Queen Mary was Queen Mother to Edward VIII and George VI, Queen Alexandra was Queen Mother to George V though neither used that as an official title. The late Queen Mother adopted the title to avoid confusion with her daughter who has the same name.
If Charles had become King during the lifetime of the Queen Mother she would revert to her previous title of Queen Elizabeth as there would then be no confusion. She would cease to be Queen Mother.
She would be Princess Elizabeth, unofficially the Queen Mother. The official description of the original Queen Mother would be Dowager Queen Mother, though this would probably not be her chosen title.
Dowager does describe a widow but also one before the title holder as it were. To illustrate, Queen Mary was still alive when her son George VI died. Queen Elizabeth became the Queen Mother on the accession of her daughter and Queen Mary's status changed from being Queen Mother to Dowager Queen Mother, the grandmother of the sovereign.
After Buck House was bombed she was said to have said: I can now look the people of the Eastend in the eye. An important difference was that she had a few other houses to move into while the people bombed out of their homes in dockland had only the clothes they stood up in.
so mucch for a priviledged lifestyle! To live life in what effetively was a goldfish bowl, told what to say and when to say it, go to places you don't want to, to see places and people you don't want to see, and all the time a photographer and TV/news camera's in youn face while you do it? No thanks! All the money jewels and titles wouldn't make me have that lifestylle.
She could have had treatment for them sandy. Even if they had to be dentures, although with modern procedures I would have thought they would have been perfect.