As a matter of fact, she hasn't. There are certain bills for which a different phrase is used (just mentioning that as a point of interest, given it's quite rare to encounter anybody who is even aware of the formal phrase). And the Queen doesn't proclaim it - the Clerk of the Parliaments does.
But she has to give consent. The United Kingdom is a Constitutional Monarchy and the Constitution gives the power to make laws to Parliament. The Monarch could only refuse assent in very extreme cases which are defined by the Lascelles Principles - and no such case has arisen during the reign of the current Queen. The last time a King even came close to refusing assent was in 1910. The last time it actually happened was in 1708.
The existence of the power prevents Parliament presenting such bills in the first place, because it would be used if it had to be.
Incidentally Her Majesty did refuse consent to a Bill in 1999 - a Bill that would have given Parliament the ability to overrule the Monarch in a dispute over whether Britain went to war or not - but that is different from refusing assent (refusal of consent stops Parliament from even debating a Bill and can only be used in the case of a few very specific royal perogatives.)
Interesting that you know the Prince of Wales. I know two people who know him (one is married to a famous actress) and neither of these two people like him.
Thanks for the history lesson.
Thank you.