Unlike peeresses crowned and anointed queen consorts hold their titles for their lives, even after being widowed. It's probably same for queens who haven't been crowned or anointed.
This was whole issue with both Queen Elizabeth and Elizabeth II having same Christian name.
In theory the sovereign would be referred to as "HM" or "Elizabeth II", but actual practice both in media and elsewhere was to refer to Elizabeth II as "the Queen". Since widowed Queen Elizabeth was also "the Queen" you can see where this was going.
Worse Queen Mary was still living when George VI died and thus was the dowager. So that couldn't be used for Queen Elizabeth even if HM wanted (and she didn't most strongly). Indeed due to her still rather young age upon being widowed Queen Elizabeth out of hand rejected much of the Victorian (if you like) ideas about widows and mourning.
People whose job it is to sort these things did some research and came up with "Queen Mother". Last holder of that title was Queen Alexandra, but don't think she used it at all.
Thus things were settled; HM, "the Queen" meant Elizabeth II and "Queen Elizabeth, The Queen Mother" was her widowed mother.
Another tidbit about queen consorts is long before commoners queens in UK were legally a mix of "feme sole" and "feme covert".
Until laws were changed not only in UK but many parts of USA as well all that a married woman had before her marriage, was to expect or actually received during was the property of her husband.
Because royal princesses dispatched to become brides of future monarchs often brought with them large to extensive amounts of property it was deemed legally necessary that they still retain some control or ownership.
Final tidbit; a peer cannot force a divorced peeress to cease using her titles. Form changes such as "The Princess of Wales" to "Diana, Princess of Wales" but that's about all a peer can hope for.
Many tried, even turning to law courts or Parliament, but decision was always same. Once a woman married and was "endowed with all his worldly goods" it included a peer's name and titles.
This was one of the reasons (among many) that Queen Elizabeth, The Queen Mother (along with others) was dead set against Wallis Simpson being made royal. It wasn't possible to restrict dukedom of Windsor to just the former king, but they made damn sure the HRH was for "David" only.
Queen Elizabeth and others were worried given Wallis Simpson's marital track record she would soon dump "David" and then there would be a thrice divorced royal duchess lose on society.
