Boondocks is on the right track.
How old is your mom? If she is an older person, then it is likely that she can't clear the effects of the drugs from her system. As we age, things just dont work as quickly as they used to.....!
Additionally the narcotic that she is undoubtedly taking for pain is prolonging the problem. However, it would be cruel to expect her to have surgery without any form of pain control.
Lastly, (again, assuming she is elderly, although could apply to any age) the change of environment on older people to that of a hospital is very stressful. There is NO SLEEP in the hospital. Nurses come in and take vital signs, hang IV medications, draw blood, all night long. The alarms and noises from monitors and other patient's IV pumps and alarms is never ending. Sleep deprivation takes a toll. This is also known to cause a sort of delerium with elderly people when they are hospitalized.
This would be the most likely scenario. HOWEVER that being said, all surgery comes with risks. And that could include major events like a stroke. So barring that the caregivers are not suspecting any sort of adverse event (ie she is moving everything and no facial droop or obvious signs of stroke), MOST of the time, the cure is.....just give it a little time and she should get back to normal once she is off of pain meds and back into a more natural routine.