Alzheimers Patient Knee Replacment Decision

My mother suffers from Alzheimers. She's living at home with care givers. Her knee pain is now to the point where she cannot walk. This is a huge decline in capability. With supervision she could walk in the park, etc. Her Dr. recommends knee replacement. Alternative treatment for pain abatement have failed, and pain medication has terrible side effects when combined with her other meds. My question; can an Alzheimers patient recover from a knee replacement procedure? How "aware" does a person have to be to do the re-hab and exercise routine? How active does a person have to be to recover? Will a sedintary life style prevent recovery? The referal surgon has few concerns, but also has very little factual knowledge of mom's capabilities. I believe the decision we have to make is a huge one in the quality of the remaining years mom has, and I don't want to screw it up. I could use any refernce material or opinions on knee replacement surgury for an Alzheimers patient. Thanks, Ed