Why wasn't Queen Elizabeth Bowes-Lyon (The Queen Mother) Elizabeth II?

Regnal numbers apply to sovereigns, and not to consorts. Before William the conqueror monarch didn't use regnal numbers, but descriptive names So before the Norman conquest you had kings: Edward the Elder Saint Edward the Martyr Saint Edward the Confessor After that they start with Edward I.

Because Elizabeth II's mother was a Queen Consort, that is, the wife of a King. She was not a Queen Regnant (that is, queen in her own right). Elizabeth II inherited the throne from her father, King George VI. If queens Consort could inherite the throne in their own right, there would have been more than three Elizabeths, Elizabeth Woodville, wife of Edward IV, would have been Elizabeth I. and Elizabeth of York, the wife of Henry VII, would have been Elizabeth II.

To put it quite simply, the consort (the spouse of a monarch) does not use the Roman Numeral at the end of their name/title. If they did, there would be 5 Elizabeths, 6 Annes, 3 Marys, 5 Catherines, 2 Margarets, 5 Matildas, and 2 Carolines. There were plenty more; I just listed the very common names of consorts.

Because she was the wife of the sovereign, not the sovereign herself. For the same reason Prince Philip isn't King Philip.

Because she was married to King George Vl

She wasn't QUEEN REGNANT. The numbers are used for those who are the regnant,the monarch in charge.Elizabeth was Queen Consort,the wife of the monarch in charge.She was a spouse,not heir to the throne,so she wasn't the Head of State,Head of Nation like Elizabeth I was,and her daughter Elizabeth II is,both being Queens Regnant.

Basically, She was Queen Elizabeth the First, Her daughter (the current Queen) being Elizabeth the Second. The Elizabeth the First that you're probably thinking about (Elizabeth Tudor 07 Sep 1533 – 24 Mar 1603) was Queen of England only and not Queen of Great Britain.

Elizabeth II is styled Elizabeth II under Royal Prerogative - and partly because the previous state, the Kingdom of England, is considered to have continued into the United Kingdom in perpetual union with Scotland. This has a legal foundation: MacCormick v Lord Advocate. MacCormick sued the Crown on the basis that Elizabeth II was not entitled to style herself Elizabeth II in Scotland because there was no Elizabeth I in Scotland. They lost on the grounds they could not actually sue the Crown, and the treaty on the Act of Union didn't mention regnal numbering. It is instead part of Royal Prerogative meaning the current monarch can choose how they are numbered. Winston Churchill suggested that monarchs should use the highest number available. That means if a James ever became King he would become James VIII - there have been 7 King James of Scotland but only 2 of England. The Queen Mother was a queen consort (married to the King) so she was not entitled to the style of a queen regnant.

A Queen only has a number if she is Queen regnant (i.e. the head of State and Queen in her own right). Queen Elizabeth, the Queen Mother was Queen Consort because her husband was King. No Queen consort had ever been numbered. (Mary II was joint monarch therefore was numbered).