To know whether knee replacement
would be successful or not for your mother, you need to get some set of physical tests done for her by a good Physiotherapists.
There are no of conditions responsible for final outcome of knee replacement-
1- Muscular strength of legs before surgery
2- Clinical condition of joint
3- Metabolic disorders
4- Post operative care and Strengthning of the replaced joint as well as entire limb
Whether other alternative treatment will work for your mother, can be said only after examining her.
If you wish you can consult me for proper guidance on alternative treatment, replacement and various other things related to her.