@chynex Hi Julia. I see you have posted before about a different issue but never having "met" you, please allow me to welcome you also.
Has your mother seen an orthopedic doctor? Is it possible that she has arthritis that has progressed to the point of needing a knee replacement? I have had two TKRs (Total Knee Replacement). Prior to having them, I was able to initially have cortisone injections which helped, and then when my arthritis progressed I got Synvisc injections which helped me tremendously. Eventually, that didn't help much anymore so I had the TKRs, one in 2013, and the second one in 2017.
If none of those are options for your mom then I guess the only other thing to help is an OTC drug like acetaminophen or ibuprofen. In acetaminophen, you can get a 650 mg dosage that is labeled for arthritis. I presume there is something like that for ibuprofen also, but since I cannot take that I have not noticed.