I hear you on the reduced physical activity... There is a couple of suggestions I can make...none of them truely fool proof but every little helps...
Bracing:
I wear wrist braces which reduces pain, but reduces the mobility in my wrists, so it reduces activity just about as much as the pain does. Not wearing them is also not an option as that would only contribute to the degeneration as I apparently have osteoarthritis...
Supplements:
Arthritis supplements, is usually available without prescription. It does seem to help. If I neglect to drink them in the morning, I sit with pain even while wearing my braces. It might be worth looking into, at least to alleaviate pain while idle.
As far as I know...and I stand corrected, the best solution a doctor would prescribe for intense pain, is cortrezone injections. Pain killers and anti-inflamatories...although effective, can be a very bad idea for long-term chronic pain relief as it will start to affect your gut, kidneys and liver.
Alternative ways to perform activities:
Some activities has solutions...others...not so easy...
I have resorted to using a pen and tablette, instead of a regular computer mouse as I can't grip it while wearing a brace. It is difficult to get used to and a bit more clumsy than the mouse but it does the job and spares my wrist.
In terms of my knees, I have come to accept the fact that I need to climb stairs slowly and carefully and it doesn't bother me as much, as I have never really been a very active person...
With my wrists, it's not so easy to accept. I can't play keyboard or piano any more as the braces don't allow the range of motion I need and playing without the braces results in pain after, sometimes as little as, fifteen minutes.
The best invention yet, has to be power-steering tho

Without it, I wouldn't be able to drive as I am sure my shoulder would have been in the same state as my wrists by now without it. It is starting to concern me though and I will most likely have to find some solution for it soon.
Let me know what the specific problem is that your sister is having...maybe I have some other suggestions
All of the best!