There is an old saying..."the show must go on." It is often recited as being in the best traditions of the stage, but in reality it is not the case.
This singer was on meds and went on ANYWAY. I will give her the benefit of the doubt that they could not find a substitute....however no performance would have been better and would have resulted in fewer views on youtube.
Medication is NEVER a good thing when you have to go on stage. Playing in pain, will at least tell you when to stop......
playing drunk? That is a story for a different day