Please do not cancel your substitute teacher at the last momnet. It is likely that she turned down other jobs after recieving the call to be in your classroom. When you cancel a job, that substitute might not be able to get another one. That means she just lost $160, which would be the ability to pay a bill or feed her family.
On a related note. If you have a preferred sub who teaches your class in a way you like, help a sistah out and take a day off once in a while! Go got your hair done. ;-)
A Substitute Teacher!