Elizabeth II and Queen Victoria are the two longest reigning monarchs but Lady Jane Grey reigned for just 9 days.
When the Queen is at home, you can see her flag, the Royal Standard, flying from the pole on top of Buckingham Palace. In flag protocol, the Royal Standard is supreme. It must only be flown from buildings where the Queen is present. It flies above the Union Jack, Standards of other Royal Family members, and other British flags. It never flies at half staff (although an exception was made following the death of Princess Diana).
The only house in England that the Queen may not enter is the House of Commons, because she is not a commoner.