No sleep could come to mind full of thoughts at that critical time (Be or Not To Be).
Queen Liza Didn't see Yzma since the early hours in the morning when Yzma came to the Queen sweet and told her that the princess Emily was about to pass away.
After YZma got her reward, a bag of golden coins, she left and never came back.
Yzma was supposed to be with the Queen at the reception of the Princes, but she disappeared.
The Queen of course didn't miss her out, but Yzma was the queen's eyes in the royal palace.
She can get all the information from everywhere, that was a very important tool in the Queen Liza hand to control everything.
More important than any maid, she was the link between the outside world and the inside palace represented by the Queen.
Whatever that Yzma was doing, the Queen never ever ever replaced her or killed her.. Noway.
The Queen still waiting