Is knee replacement worth it?

My mother ( age 46, 260 lbs) slipped an fell on ice about 2 yrs ago. She dislocated a plate in her back, and tore ligaments in her right knee. She has had 2 surgeries to fix the damage, but neither was successful. Knee replacement has been brought up but she has no interest at all of doing it. But i feel that it needs to be done. Her weight doesn't help her knee, but b/c of her knee she is unable to do any physical activity, therefore gaining more weight. Its become one big spiraling hole. I just want some opinions on knee replacement, and maybe some help in to talking her into it. The hole idea of not being able to do anything for a while in order to heal stresses her. But she cant even do anything now. her knee is so swollen, and she is in so much pain. What are the pros and cons of knee replacement. What are the risks, what are the benefits. She needs help. Her health is deteriorating quickly.