It's a standard twitter troll with a standard twitter prank

1. Make a fake account and set it to private
2. Run a bot that will tweet "The Queen will die on [date]" thousands of times, each with a different date counting several years ahead (doesn't need to be infinite, she won't live for hundreds of years so 10-15 years will do)
3. When she eventually does die, have the bot delete all the other wrong dates and just leave the right one then put the profile on public.
4. People won't find the deleted tweets because it was set to private before. Hence they will yhink it's legit.
5. Sit back and have fun! People will be trying to decipher your other random made-up criptic bullshit tweets and you can secretly laugh at them.